[libc][obvious] fix missed rename

[michaelrj]

Summary

In https://reviews.llvm.org/D114302 I renamed ForLoopCopy to
for_loop_copy, but these got missed.

libc/src/string/memory_utils/elements.h

 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
 #endif
 
 template <size_t Size> struct Builtin {
   static constexpr size_t SIZE = Size;
 
   static void copy(char *__restrict dst, const char *__restrict src) {
 #if LLVM_LIBC_HAVE_MEMORY_SANITIZER || LLVM_LIBC_HAVE_ADDRESS_SANITIZER
-    ForLoopCopy(dst, src);
+    for_loop_copy(dst, src);
 #elif __has_builtin(__builtin_memcpy_inline)
     // __builtin_memcpy_inline guarantees to never call external functions.
     // Unfortunately it is not widely available.
     __builtin_memcpy_inline(dst, src, SIZE);
 #elif __has_builtin(__builtin_memcpy)
     __builtin_memcpy(dst, src, SIZE);
 #else
-    ForLoopCopy(dst, src);
+    for_loop_copy(dst, src);
 #endif
   }
 
   static void move(char *dst, const char *src) {
 #if LLVM_LIBC_HAVE_MEMORY_SANITIZER || LLVM_LIBC_HAVE_ADDRESS_SANITIZER
     for_loop_move(dst, src);
 #elif __has_builtin(__builtin_memmove)
     __builtin_memmove(dst, src, SIZE);