llvm-project

3c532a4f - [libc] Add POSIX regex stub implementation and build infrastructure (#196995)

[libc] Add POSIX regex stub implementation and build infrastructure (#196995) Added the four POSIX regex entrypoints (regcomp, regexec, regerror, regfree) and registered them for x86_64, aarch64, riscv, and arm. regerror is fully implemented with all 13 POSIX error code strings. The other three are stubs backed by simple string matching to validate the build pipeline end-to-end. This implementation is restricted to full-build mode (LLVM_LIBC_FULL_BUILD) to avoid ABI compatibility risks with system headers and internal state management in overlay mode. New files: * include/regex.yaml and regex-macros.h for header generation * regex_t, regoff_t, regmatch_t type headers * src/regex/ with all four entrypoints * test/src/regex/ with regerror and basic round-trip tests All 7 tests pass.