build: guard feature macros under -Wundef

[isuzano]

Summary

Fix -Wundef failures caused by optional compiler/platform macros being used without guards.

Changes

• Add fallback for __has_ptrcheck
• Use defined(...) guards for compiler/platform macros
• Fix __ZX_FIXED_ENUMS fallback without macro redefinition
• Adjust __APPLE__ and __clang__ checks

Validation

• make clean: OK
• make test: progresses past previous -Wundef failures
• Remaining failure is unrelated: -Wstack-protector in unit_buff_write_object_flex.c

Notes

This patch does not emulate bounds-safety features and does not change runtime behavior.
It only ensures safe handling of feature-test macros under -Wundef.

[isuzano]

@microsoft-github-policy-service agree

[mingodad]

With this changes my build with gcc9 goes further but dies with:

make
cc -std=gnu11 -Werror -Wall -Wextra -Wcast-qual -Wconversion -Wformat=2 -Wformat-security -Wnull-dereference -Wstack-protector -Wvla -Warray-bounds -Wimplicit-fallthrough -Wint-conversion -Wdouble-promotion -Wundef -Wstrict-prototypes -Wbad-function-cast -Wfloat-equal -Wpointer-arith -Wformat-truncation=2 -Wformat-signedness -Wuninitialized -Wlogical-op -Wduplicated-cond -Wduplicated-branches -fstack-protector-strong -fno-delete-null-pointer-checks -ftrapv -Isrc -Iposix -g -DTARGET_0XTEST=1 -DPOINTER_TAG_BITS_HI=16 -DPOINTER_TAG_BITS_LO=3  -c -o build/public/obj/lib/src/0xc/std/cursor.o src/0xc/std/cursor.c
In file included from src/0xc/std/cursor.c:12:
src/0xc/std/cursor.c: In function ‘cmemopen’:
src/0xc/std/string.h:129:2: error: implicit declaration of function ‘strlcpy’; did you mean ‘strncpy’? [-Werror=implicit-function-declaration]
  129 |  strlcpy((DST), (SRC), sizeof(DST)); \
      |  ^~~~~~~
src/0xc/std/cursor.c:45:2: note: in expansion of macro ‘strscpy’
   45 |  strscpy(cur->cur_mode, mode);
      |  ^~~~~~~
cc1: all warnings being treated as errors
Makefile.public:148: recipe for target 'build/public/obj/lib/src/0xc/std/cursor.o' failed
make: *** [build/public/obj/lib/src/0xc/std/cursor.o] Error 1

Maybe it's missing some linux glibc specific definitions.

[SIGFUN]

With this changes my build with gcc9 goes further but dies with:

make
cc -std=gnu11 -Werror -Wall -Wextra -Wcast-qual -Wconversion -Wformat=2 -Wformat-security -Wnull-dereference -Wstack-protector -Wvla -Warray-bounds -Wimplicit-fallthrough -Wint-conversion -Wdouble-promotion -Wundef -Wstrict-prototypes -Wbad-function-cast -Wfloat-equal -Wpointer-arith -Wformat-truncation=2 -Wformat-signedness -Wuninitialized -Wlogical-op -Wduplicated-cond -Wduplicated-branches -fstack-protector-strong -fno-delete-null-pointer-checks -ftrapv -Isrc -Iposix -g -DTARGET_0XTEST=1 -DPOINTER_TAG_BITS_HI=16 -DPOINTER_TAG_BITS_LO=3  -c -o build/public/obj/lib/src/0xc/std/cursor.o src/0xc/std/cursor.c
In file included from src/0xc/std/cursor.c:12:
src/0xc/std/cursor.c: In function ‘cmemopen’:
src/0xc/std/string.h:129:2: error: implicit declaration of function ‘strlcpy’; did you mean ‘strncpy’? [-Werror=implicit-function-declaration]
  129 |  strlcpy((DST), (SRC), sizeof(DST)); \
      |  ^~~~~~~
src/0xc/std/cursor.c:45:2: note: in expansion of macro ‘strscpy’
   45 |  strscpy(cur->cur_mode, mode);
      |  ^~~~~~~
cc1: all warnings being treated as errors
Makefile.public:148: recipe for target 'build/public/obj/lib/src/0xc/std/cursor.o' failed
make: *** [build/public/obj/lib/src/0xc/std/cursor.o] Error 1

Maybe it's missing some linux glibc specific definitions.

Do you have prototypes for strlcpy(3) et al. in your default search paths? Might need to add an inclusion path depending on your system if the gcc9 toolchain headers don't have those prototypes.

[SIGFUN]

Thanks!