Switch from C headers to C++ headers.

This CL makes the following substitutions.

* assert.h -> cassert
* math.h -> cmath
* stdarg.h -> cstdarg
* stdio.h -> cstdio
* stdlib.h -> cstdlib
* string.h -> cstring

stddef.h and stdint.h are not migrated to C++ headers.

PiperOrigin-RevId: 309074805

snappy-test.h

@@ -31,14 +31,13 @@
 #ifndef THIRD_PARTY_SNAPPY_OPENSOURCE_SNAPPY_TEST_H_
 #define THIRD_PARTY_SNAPPY_OPENSOURCE_SNAPPY_TEST_H_
 
+#include <cstdarg>
+#include <cstdio>
 #include <iostream>
 #include <string>
 
 #include "snappy-stubs-internal.h"
 
-#include <stdio.h>
-#include <stdarg.h>
-
 #ifdef HAVE_SYS_MMAN_H
 #include <sys/mman.h>
 #endif