sdk: report Kandelo's musl userland truthfully to Autoconf

[brandonpayton]

Why

The software development kit (SDK) identifies Kandelo to package configure scripts. musl is Kandelo's C standard library, while GNU Autoconf and gnulib use the reported target name to choose compatible source code.

Report the SDK's real musl userland identity to GNU build systems so Autoconf and gnulib choose musl behavior instead of treating Kandelo as an unknown libc.

GNU M4 made the mismatch visible: wasm32posix-configure reported --host=wasm32-unknown-none, so gnulib did not define MUSL_LIBC even though the SDK links musl. Correcting the identity also exposed an upstream PHP cross-compilation assumption: PHP treats every *linux* host as glibc and selects an off64_t * fopencookie callback, while musl truthfully uses off_t *.

What changed

• Use wasm*-unknown-linux-musl as the GNU/Autoconf host identity.
• Keep wasm*-unknown-unknown as Clang's code-generation triple.
• Name, document, and test those two separate contracts for wasm32 and wasm64.
• In PHP's generated cross-build config, preserve real HAVE_FOPENCOOKIE support but undefine only the glibc-specific COOKIE_SEEKER_USES_OFF64_T choice.
• Fail the PHP build if either generated-header invariant is lost, and force the affected stream-casting object to rebuild.

GNU config.sub requires a Linux kernel component for a musl tuple. This describes the musl userland; it does not define __linux__, change Kandelo's syscall contract, or promise Linux kernel behavior. The PHP adjustment is an upstream cross-compilation compatibility fix, not a substitute for missing Kandelo functionality.

Validation

Final candidate: a98bd0d7235075e638aab779ee4785cc44e6e78b (tree 0feb3d28b7aac6e7bd0a85da7d31a5eae638639e).

• The exact final head built PHP 8.3.15 CLI, FPM, and all declared extensions from source after both fopencookie assertions passed.
• The resulting php.wasm and php-fpm.wasm were optimized, fork-instrumented, and validated as ABI 39 program artifacts.
• After a fresh ABI-39 rootfs build, the focused Kandelo runtime test executed the freshly rebuilt php -r artifact and passed.
• A direct SDK compile confirmed musl accepts the off_t * callback and rejects PHP's glibc-only off64_t * callback.
• SDK Vitest on the preceding target-identity head passed 7 files and 74 tests, including sdk: preserve static linker argument order #913 linker-order and sdk: centralize cross-compile function availability #874 target-fact coverage.
• ABI consistency passed; this changes no ABI surface.
• Final-head bash -n and git diff --check passed.
• Independent review accepted the exact final head and confirmed the PHP correction belongs with the target-identity change.

Hosted staging is running on this exact head. The preceding run rebuilt curl with the truthful wasm32-unknown-linux-musl identity and exposed one stale registry test expectation; that expectation is now folded into the original target-identity commit. The other 1,406 Vitest cases and the package/library matrix passed in that run.

Consumer evidence on the earlier target-identity head also includes source builds and literal Kandelo runtime tests for GNU Grep, GNU Sed, GNU M4, and XZ.

Contract impact

This changes SDK configure metadata and one upstream PHP cross-build decision. It changes no syscall, channel, memory layout, host runtime, browser behavior, or ABI version. Node and browser hosts consume the same resulting Wasm contract.

Merge ordering

This PR is stacked on #874, which is stacked on #913. Merge #913, then #874, then retarget this PR to main. GNU M4 and other consumers require #874's authoritative sdk/config.site facts beneath this host identity; without them, Kandelo's allow-undefined link mode can create false-positive function probes.

This is a main-repository PR for review and must not be auto-merged.

[github-actions]

Phase B-1 matrix build status — pr-883-staging

ABI v39. 71 built, 0 failed, 71 total.

Package	Arch	Status	Sha
icu	wasm32	built	5ff9ee8d
libcurl	wasm32	built	0b1b1671
libcxx	wasm32	built	264bead6
libcxx	wasm64	built	0a1af93a
libiconv	wasm32	built	560b07f2
libpng	wasm32	built	eb91c16b
libxml2	wasm32	built	f7b57dc8
libzip	wasm32	built	81c1337b
openssl	wasm32	built	c08ae93b
openssl	wasm64	built	73478b9f
sqlite	wasm32	built	21ab1f0c
sqlite	wasm64	built	bb235497
zlib	wasm32	built	242b4b6c
zlib	wasm64	built	277c6ac7
bc	wasm32	built	d26e2827
bzip2	wasm32	built	ec8d1452
coreutils	wasm32	built	63821f2c
curl	wasm32	built	095be673
dash	wasm32	built	417065a9
diffutils	wasm32	built	d0f1fde0
dinit	wasm32	built	18d4e737
fbdoom	wasm32	built	23d90bea
file	wasm32	built	106ea18c
findutils	wasm32	built	84ae9303
gawk	wasm32	built	2e0cbf19
git	wasm32	built	32505568
grep	wasm32	built	86e9a832
gzip	wasm32	built	87e3edf0
hello	wasm32	built	eeda49a5
kandelo-sdk	wasm32	built	1c07b3f1
kernel	wasm32	built	66f5a872
less	wasm32	built	82cf7855
lsof	wasm32	built	813e02a9
m4	wasm32	built	c5c145bd
make	wasm32	built	bb0baede
mariadb	wasm32	built	4c9d0701
mariadb	wasm64	built	c40f13e1
modeset	wasm32	built	f6bf2b67
msmtpd	wasm32	built	65978078
nano	wasm32	built	520fca7a
ncurses	wasm32	built	549cc665
netcat	wasm32	built	9bc9ff6c
nginx	wasm32	built	fb5d0866
php	wasm32	built	506473b2
posix-utils-lite	wasm32	built	cab59030
ruby	wasm32	built	3f1d1019
sed	wasm32	built	73ee890d
spidermonkey	wasm32	built	59cda6fd
tar	wasm32	built	19723213
tcl	wasm32	built	82b99ef7
unzip	wasm32	built	ebf0baaf
userspace	wasm32	built	6195dcb4
vim	wasm32	built	61c88ab1
wget	wasm32	built	d45f15b8
xz	wasm32	built	62b860c9
zip	wasm32	built	589eaae7
zstd	wasm32	built	3b57442d
bash	wasm32	built	727ab35e
mariadb-test	wasm32	built	53c2d150
mariadb-vfs	wasm32	built	bf4404a8
mariadb-vfs	wasm64	built	9fd67b54
nethack	wasm32	built	da9c9092
node	wasm32	built	ffbc0dab
spidermonkey-node	wasm32	built	532c3d92
vim-browser-bundle	wasm32	built	678247c1
nethack-browser-bundle	wasm32	built	56b84057
rootfs	wasm32	built	91af3bbe
shell	wasm32	built	daae0d15
lamp	wasm32	built	60ccb85d
node-vfs	wasm32	built	918187b5
wordpress	wasm32	built	65df6293

_{Auto-generated; replaced on each push. Raw data in the publish-status workflow artifact.}

[brandonpayton]

Controlled Homebrew consumer evidence at exact head ac91610ca484bae679bd6eb08a6e1bcfed47d111:

• Baseline integration 937dd19f2574724732b9b4e0b7af98911cd7e568 contains exact sdk: centralize cross-compile function availability #874 (1150cfa4) and Reject stale Wasm artifacts with aliased ABI exports #882 (ad671bb4), but not sdk: report Kandelo's musl userland truthfully to Autoconf #883. The unchanged live-tap GNU M4 1.4.21 formula configured as wasm32-unknown-none, left MUSL_LIBC undefined, and failed in getlocalename_l-unsafe.c:662 with the explicit Gnulib porting error.
• Merging exact sdk: report Kandelo's musl userland truthfully to Autoconf #883 into that same integration as d72b296a4c0c514bcb6b826f3652b87154357863 changed the Autoconf host identity to wasm32-unknown-linux-musl and defined MUSL_LIBC=1. The same live formula then completed configure, make, and install: 14 files / 1.2 MB, 54 seconds, exit 0.

No tap formula workaround such as -DMUSL_LIBC was present: the installed Cellar recipe is byte-identical to the live formula (SHA-256 29d490bdb9c272b0c561cd764a9f4784a8284a12b74c460163147e2f7bb9f73a). No ABI change was used. This is source-build evidence only; it does not claim a bottle or guest pour.

[brandonpayton]

Absorbed by rebase-merged #967. Main is now 6efb411 with the sealed tree b133bfa018f7e2bc84c4845edf2f945b2f844954, and ABI 41 activation completed successfully in run 29550069085. The absorption audit confirmed this PR\x27s behavior and tests are present in that merged tree, so this source PR is closed and its branch is deleted.