Revert "[libc++] Refactoring __sync_* builtins; NFC (Reland)"

This reverts commit r307595. The commit had some issues that needed
to first be addressed in review.

llvm-svn: 307746
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: e82f49849b259c9e6dd2b310fb5e46c0c2ee306a
diff --git a/include/__refstring b/include/__refstring
index de89b79..7f417a0 100644
--- a/include/__refstring
+++ b/include/__refstring
@@ -14,7 +14,6 @@
 #include <stdexcept>
 #include <cstddef>
 #include <cstring>
-#include <__atomic_support>
 #ifdef __APPLE__
 #include <dlfcn.h>
 #include <mach-o/dyld.h>
@@ -84,7 +83,7 @@
     : __imp_(s.__imp_)
 {
     if (__uses_refcount())
-        __libcpp_sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
 }
 
 inline
@@ -93,10 +92,10 @@
     struct _Rep_base *old_rep = rep_from_data(__imp_);
     __imp_ = s.__imp_;
     if (__uses_refcount())
-        __libcpp_sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
     if (adjust_old_count)
     {
-        if (__libcpp_sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
+        if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
         {
             ::operator delete(old_rep);
         }
@@ -108,7 +107,7 @@
 __libcpp_refstring::~__libcpp_refstring() {
     if (__uses_refcount()) {
         _Rep_base* rep = rep_from_data(__imp_);
-        if (__libcpp_sync_add_and_fetch(&rep->count, count_t(-1)) < 0) {
+        if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0) {
             ::operator delete(rep);
         }
     }