[RAI-47876] Hard-code semaphore name to avoid thread-unsafe getenv calls

[bunjj]

Problem

Parallel precompilation semaphore coordination was using getenv("JL_AOT_PRECOMPILE_SEMAPHORE") to get the semaphore name. This caused thread-unsafe races with setenv/unsetenv calls in the parent Julia process, leading to segfaults in tests.

Related: JuliaLang#34726

Solution

Hard-code the semaphore name to /jl_aot_par_precomp_semaphore instead of reading from ENV:

• Always try sem_open("/jl_aot_par_precomp_semaphore", 0) (without O_CREAT)
• If semaphore exists: use it for coordination (compcache path)
• If semaphore doesn't exist: skip coordination (normal compilation path)

Changes

• src/aotcompile.cpp: Removed getenv call, hard-coded semaphore name, restructured logic

Dependencies

Paired with RAICode PR: https://github.com/RelationalAI/raicode/pull/27411