The previous commits used gmtime_r/localtime_r (unavailable on Windows)
and assumed the GNU strerror_r variant returning char* (only on glibc).
This broke macOS, musl, WASM, and Win32 builds.
Add userspace/engine/compat.h with portable inline wrappers:
- falco_gmtime_r / falco_localtime_r: use gmtime_s/localtime_s on Win32
- falco_strerror_r: returns const char* on all platforms, detecting
glibc via __GLIBC__ (not _GNU_SOURCE alone, since musl defines
_GNU_SOURCE but provides the XSI variant returning int)
Also fixes a pre-existing bug in create_signal_handlers.cpp where
the GNU strerror_r return value was incorrectly compared to 0 and
the actual error string was discarded.
Signed-off-by: Leonardo Grasso <me@leonardograsso.com>
abdf5512c8