Compile postgres

[rennergade]

Closes #65

Summary

• Cross-compile the PostgreSQL backend (postgres) and initdb to wasm32-wasi using a two-pass build strategy (native pass for flex/bison/Perl codegen, then WASM cross-compile)
• Add make postgres / make install-postgres targets to the top-level Makefile
• Produce postgres.wasm → postgres.cwasm (and initdb.wasm → initdb.cwasm when initdb links successfully)

Notable / Weird Build Workarounds

• Two-pass build (like bash): PostgreSQL's build generates C/H files with flex, bison, and Perl scripts that must run natively. Pass 1 builds these on the host, then we clean .o files while preserving the generated sources and re-configure for WASM in Pass 2.
• Config cache (config.cache.wasi): Cross-compile configure can't run test programs, so we pre-populate a cache with type sizes, alignments, spinlock support, and function availability for the wasm32 ILP32 target.
• Makefile.shlib patched to disable shared libraries: wasm-ld cannot build .so files (no --version-script, --shared incompatible with --export-memory, missing crt1-reactor.o). We comment out the all-shared-lib dependency so only static libpq.a is produced.
• libpq/Makefile patched: libpq-refs-stamp normally depends on the shared lib and runs a Perl symbol check. We remove that dependency since there’s no .so to check.
• pg_config.h patched post-configure: Force-disable EXEC_BACKEND (no fork), all semaphore types (stubbed), and ensure HAVE_SPINLOCKS is set (GCC atomic builtins work on WASM).
• Root-user check patched out in main.c: Lind sandbox’s geteuid() returns 0, but the security concern does not apply inside the sandbox.
• wasm_compat.h force-included: Maps old st_atime / st_mtime / st_ctime stat field names to WASI’s st_atim.tv_sec / st_mtim.tv_sec / st_ctim.tv_sec.
• wasi_stubs.c: Stubs _Unwind_Backtrace, _Unwind_GetIP, _Unwind_GetGR, _Unwind_GetCFA. These are pulled in by glibc’s backtrace.o, but WASI has no stack unwinder.
• initdb link flags manually specified: The compile script overrides LIBS on the make command line (to inject wasi_stubs.o -lm), which wipes out -lpgcommon -lpgport that configure normally adds. We re-add them along with explicit -L paths since the LDFLAGS override also drops LDFLAGS_INTERNAL.
• 256 MB --max-memory: PostgreSQL allocates shared buffers even in single-user mode and needs more than the default.
• Best-effort throughout: Backend, libpq, fe_utils, and initdb builds all tolerate errors and continue.

New Files

• postgres/compile_postgres.sh — main build orchestrator (527 lines)
• postgres/wasi_stubs.c — _Unwind_* no-op stubs
• postgres/wasm_compat.h — stat field name compatibility macros

Test Plan

• make postgres completes and produces postgres.cwasm in build/bin/postgres/wasm32-wasi/
• initdb.cwasm is also produced (or at least link errors are diagnosed and documented)
• lind-boot can load and start the postgres binary in single-user mode

[rennergade]

This runs but basically doesn't do anything, a lot to debug here.

lind@894575b27c0f:~/lind-wasm/lindfs$ lind-wasm bin/postgres
LOG:  invalid binary "bin/postgres": Permission denied
LOG:  invalid binary "bin/postgres": Permission denied
FATAL:  bin/postgres: could not locate my own executable path