Added nullptr handling to wmemcmp

Author: Sriya Pratipati

libc/src/wchar/wmemcmp.cpp

@@ -12,11 +12,14 @@
 #include "hdr/types/wchar_t.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h" // LIBC_CRASH_ON_NULLPTR
 
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, wmemcmp,
                    (const wchar_t *s1, const wchar_t *s2, size_t n)) {
+  LIBC_CRASH_ON_NULLPTR(s1);
+  LIBC_CRASH_ON_NULLPTR(s2);
   for (size_t i = 0; i < n; ++i) {
     if (s1[i] != s2[i])
       return (int)(s1[i] - s2[i]);