Cherry-pick compiler compatibility fixes from upstream#63

Merged

kornelski merged 5 commits intogcc.amd64from

Mar 11, 2025

Commits on Mar 11, 2025

Remove fdopen #defines in zutil.h.

madler
authored and
kornelski
committed
Use _POSIX_C_SOURCE in gzguts.h, instead of _POSIX_SOURCE.

madler
authored and
kornelski
committed
Assume no snprintf() or vsnprintf() if C89/90 in gzguts.h.

madler
authored and
kornelski
committed
Use z_const for setting msg to literal strings.

Lwisce Zeng
authored and
kornelski
committed
Reject invalid MAX_WBITS values at compile time.

madler
authored and
kornelski
committed