[compiler-rt] Fix AArch64 out-of-line atomics visibility on mach-o

This fixes an apparent oversight in D91156, where the symbol was defined
without the leading underscore, then the visibility was later declared with it.
rdar://73364185

Differential revision: https://reviews.llvm.org/D95639

GitOrigin-RevId: 5f3c4923e4e4d5f40a64e08e407067ff551f2901
diff --git a/lib/builtins/assembly.h b/lib/builtins/assembly.h
index f6ce6a9..80287f2 100644
--- a/lib/builtins/assembly.h
+++ b/lib/builtins/assembly.h
@@ -204,8 +204,11 @@
 #ifdef VISIBILITY_HIDDEN
 #define DECLARE_SYMBOL_VISIBILITY(name)                                        \
   HIDDEN(SYMBOL_NAME(name)) SEPARATOR
+#define DECLARE_SYMBOL_VISIBILITY_UNMANGLED(name) \
+  HIDDEN(name) SEPARATOR
 #else
 #define DECLARE_SYMBOL_VISIBILITY(name)
+#define DECLARE_SYMBOL_VISIBILITY_UNMANGLED(name)
 #endif
 
 #define DEFINE_COMPILERRT_FUNCTION(name)                                       \
@@ -248,7 +251,7 @@
   FUNC_ALIGN                                                                   \
   .globl name SEPARATOR                                                        \
   SYMBOL_IS_FUNC(name) SEPARATOR                                               \
-  DECLARE_SYMBOL_VISIBILITY(name) SEPARATOR                                    \
+  DECLARE_SYMBOL_VISIBILITY_UNMANGLED(name) SEPARATOR                          \
   CFI_START SEPARATOR                                                          \
   DECLARE_FUNC_ENCODING                                                        \
   name: SEPARATOR BTI_C