MSan doesn't seem to instrument parse_printf_format

[evverx]

One of systemd fuzzers triggers a "use-of-uninitialized-value" warning, which I'm going to get around by manually initializing the array MSan is complaining about. I opened the issue here mostly because I need something to refer to in the commit message.

root@1c59ccf2eb06:/src/systemd# clang --version
clang version 7.0.0 (trunk 338452)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin

root@1c59ccf2eb06:/src/systemd# cat test.c
#include <printf.h>
#include <stdio.h>

int main(int arc, char *argv[]) {
	int _argtypes[128];
	size_t _i, _k;
	_k = parse_printf_format("%s", 128, _argtypes);
	for (_i = 0; _i < _k; _i++)
		if (_argtypes[_i] & PA_FLAG_PTR) {
			printf("Found a pointer\n");
	}
	return 0;
}

root@1c59ccf2eb06:/src/systemd# clang -fsanitize-memory-track-origins -g -fsanitize=memory ./test.c -o a.out

root@1c59ccf2eb06:/src/systemd# ./a.out
==183==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x49bdaa in main /src/systemd/./test.c:9:7
    #1 0x7f5eda5aa82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #2 0x41ae08 in _start (/src/systemd/a.out+0x41ae08)

  Uninitialized value was created by an allocation of '_argtypes' in the stack frame of function 'main'
    #0 0x49b770 in main /src/systemd/./test.c:4

SUMMARY: MemorySanitizer: use-of-uninitialized-value /src/systemd/./test.c:9:7 in main
Exiting