C: crtl headers miss libc syscall prototypes (fsync, …)

• Type: bug / gap (C frontend → crtl headers) — Track C/B boundary
• Status: done
• Owner: Track CA
• Found / Opened: 2026-06-27, M5 sqlite bring-up ([[feature-c-desktop-lua-sqlite-path]]). Wall after the fn-ptr cast-call fix.
• Closed: 2026-06-27

Symptom

pascal26:31615: error: call to undeclared function: fsync ()

sqlite's unix VFS calls fsync, fchmod, fchown, geteuid, read, write, close, lseek, unlink, mmap, … expecting <unistd.h> / <fcntl.h> / <sys/mman.h> to declare them. pxx's crtl headers (lib/crtl/include) declare some libc functions but not these, so the call hits the "call to undeclared function" path instead of an extern libc import.

Likely shape of the fix

Two angles, not mutually exclusive:

1. (Track B — lib/crtl) add the missing POSIX prototypes to the crtl unistd.h / fcntl.h / sys/*.h so the names resolve to libc externs (the C extern-binds-libc path already works for open/printf). This is the lib-side, file-ownership-correct home for header content.
2. (Track C — cparser) optionally support C89 implicit declaration: an undeclared name(args) call synthesises an extern int name() cdecl import (libc) rather than erroring. sqlite does include the headers, so (1) is the faithful fix; (2) is a broader convenience and a policy call.

Fix

Added the narrow sqlite-needed POSIX declarations to lib/crtl/include/unistd.h: fsync, sysconf, and _SC_PAGESIZE / _SC_PAGE_SIZE. These declarations feed the existing C header prototype path, which registers libc extern imports.

The sqlite compile now advances past fsync at 31615 and sysconf(_SC_PAGESIZE) at 42642, then stops at a separate C preprocessor defined(...) conditional wall near the unix VFS locking-style block.

Regression

Added test/crtl_unistd_fsync_b99.c, wired into make test-core.

Repro

int main(void){ return fsync(1); }   /* no #include <unistd.h> */

Acceptance

• sqlite advances past 31615; fsync and sysconf resolve to libc imports.
• A crtl-header smoke test covers the added prototypes.