Add NullChecks to strspn.cpp

Author: AlyElashram

libc/src/string/strspn.cpp

@@ -11,11 +11,14 @@
 #include "src/__support/CPP/bitset.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
 #include <stddef.h>
 
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(size_t, strspn, (const char *src, const char *segment)) {
+  LIBC_CRASH_ON_NULLPTR(src);
+  LIBC_CRASH_ON_NULLPTR(segment);
   const char *initial = src;
   cpp::bitset<256> bitset;