[clang-tidy] C to C++ headers

Found with modernize-deprecated-headers

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/builtin_string.cpp

@@ -5,15 +5,13 @@
 #ifdef _WIN32
 #define PCRE2_STATIC
 #endif
-#include <errno.h>
-#include <limits.h>
-#include <stdarg.h>
-#include <stddef.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <wctype.h>
-
 #include <algorithm>
+#include <cerrno>
+#include <climits>
+#include <cstdarg>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
 #include <cwchar>
 #include <cwctype>
 #include <iterator>