[PAC] `ptrauth.h` triggers `-Wgnu-statement-expression-from-macro-expansion`

[EliaGeretto]

When including ptrauth.h without using -fptrauth-intrinsics, -Wgnu-statement-expression-from-macro-expansion is triggered. That warning is part of -Wpedantic.

The issue is caused by the use of GNU statement expressions in the following macro:

llvm-project/clang/lib/Headers/ptrauth.h

Lines 329 to 333 in 6b58449

	#define ptrauth_strip(__value, __key) \
	({ \
	(void)__key; \
	__value; \
	})

A possible fix is relying on the comma operator:

 #define ptrauth_strip(__value, __key)                                          \
   (                                                                            \
     (void)__key,                                                               \
     __value                                                                    \
   )

Reproducer:

#include <ptrauth.h>

int main(void) {
    ptrauth_strip(&main, ptrauth_key_function_pointer);
    return 0;
}

Build with: clang -Wpedantic repro.c

[efriedma-quic]

CC @ojhunt @ahmedbougacha @ahatanak