[libc][NFC] move strcoll to strcmp template

[michaelrj]

Summary

While locales are not implemented, strcoll is equivalent to strcmp. This
patch moves strcoll over to the strcmp internal implementation.

[mcgrathr]

Is there a reason not to just call __llvm_libc::strcmp ?
The two will likely get collapsed by --icf=all anyway, but making it just a tail call to start with seems ideal.

[michaelrj]

Currently we're avoiding calling functions by their public name inside of other implementations when possible to keep each entrypoint independent.

libc/src/string/CMakeLists.txt

 )
 
 add_entrypoint_object(
   strcoll
   SRCS
     strcoll.cpp
   HDRS
     strcoll.h
+  DEPENDS
+    .memory_utils.strcmp_implementation
 )
 
 add_entrypoint_object(
   strcpy
   SRCS
     strcpy.cpp
   HDRS
     strcpy.h

libc/src/string/strcoll.cpp

 //===-- Implementation of strcoll -----------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "src/string/strcoll.h"
 
 #include "src/__support/common.h"
+#include "src/string/memory_utils/strcmp_implementations.h"
 
 namespace __llvm_libc {
 
 // TODO: Add support for locales.
 LLVM_LIBC_FUNCTION(int, strcoll, (const char *left, const char *right)) {
-  for (; *left && *left == *right; ++left, ++right)
-    ;
-  return static_cast<int>(*left) - static_cast<int>(*right);
+  auto comp = [](char l, char r) -> int {
+    return static_cast<int>(l) - static_cast<int>(r);
+  };
+  return strcmp_implementation(left, right, comp);
 }
 
 } // namespace __llvm_libc