Fix invalid function pointer cast in cpuinfo.c

While casting function pointers is allowed in C, the function must
ultimately be called through a pointer with the same type signature as
the function itself. Type signature mismatches, even decaying T* to
void* is undefined behavior.

UBSan flags this with -fsanitize=function. The easiest way I found to
repro this was:

    CC=clang-18 CXX=clang++-18 \
    CFLAGS="-fsanitize=function -fno-sanitize-recover=function" \
    CXXFLAGS="-fsanitize=function -fno-sanitize-recover=function" \
    cmake -GNinja -B build -DCPUINFO_BUILD_BENCHMARKS=OFF

    ninja -C build

    ./build/cpu-info

That gives the following error:

    [...]/src/linux/multiline.c:85:11: runtime error: call to function parse_line through pointer to incorrect function type 'bool (*)(const char *, const char *, void *, unsigned long)'
    cpuinfo.c: note: parse_line defined here
    SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior [...]/src/linux/multiline.c:85:11

The fix is fairly straightforward: just keep the function at the type
signature the expected, and cast void* instead the function instead.

Author: davidben

src/x86/linux/cpuinfo.c

@@ -83,8 +83,9 @@ struct proc_cpuinfo_parser_state {
 static bool parse_line(
 	const char* line_start,
 	const char* line_end,
-	struct proc_cpuinfo_parser_state state[restrict static 1],
+	void* context,
 	uint64_t line_number) {
+	struct proc_cpuinfo_parser_state* restrict state = context;
 	/* Empty line. Skip. */
 	if (line_start == line_end) {
 		return true;
@@ -215,5 +216,5 @@ bool cpuinfo_x86_linux_parse_proc_cpuinfo(
 		.processors = processors,
 	};
 	return cpuinfo_linux_parse_multiline_file(
-		"/proc/cpuinfo", BUFFER_SIZE, (cpuinfo_line_callback)parse_line, &state);
+		"/proc/cpuinfo", BUFFER_SIZE, parse_line, &state);
 }