Add a VISIBILITY_HIDDEN option, which can be used to make all compiler-rt function definitions hidden/private extern.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@93790 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/assembly.h b/lib/assembly.h
index e6b8410..c2d5a34 100644
--- a/lib/assembly.h
+++ b/lib/assembly.h
@@ -30,9 +30,16 @@
 #define SYMBOL_NAME(name) name
 #endif
 
+#ifdef VISIBILITY_HIDDEN
+#define DEFINE_COMPILERRT_FUNCTION(name) \
+  .globl SYMBOL_NAME(name) SEPARATOR     \
+  .private_extern SYMBOL_NAME(name) SEPARATOR    \
+  SYMBOL_NAME(name):
+#else
 #define DEFINE_COMPILERRT_FUNCTION(name) \
   .globl SYMBOL_NAME(name) SEPARATOR     \
   SYMBOL_NAME(name):
+#endif
 
 #define DEFINE_COMPILERRT_PRIVATE_FUNCTION(name) \
   .globl SYMBOL_NAME(name) SEPARATOR             \