Set symbol visibility to hidden.

Not doing so may cause all sorts of random libraries to expose
libcompiler_rt's functions, which should of course not be done.

Discussed with:	kan, kib

contrib/compiler-rt/lib/assembly.h

@@ -33,7 +33,7 @@
 #ifdef VISIBILITY_HIDDEN
 #define DEFINE_COMPILERRT_FUNCTION(name) \
   .globl SYMBOL_NAME(name) SEPARATOR     \
-  .private_extern SYMBOL_NAME(name) SEPARATOR    \
+  .hidden SYMBOL_NAME(name) SEPARATOR    \
   SYMBOL_NAME(name):
 #else
 #define DEFINE_COMPILERRT_FUNCTION(name) \
@@ -43,12 +43,12 @@
 
 #define DEFINE_COMPILERRT_PRIVATE_FUNCTION(name) \
   .globl SYMBOL_NAME(name) SEPARATOR             \
-  .private_extern SYMBOL_NAME(name) SEPARATOR    \
+  .hidden SYMBOL_NAME(name) SEPARATOR    \
   SYMBOL_NAME(name):
 
 #define DEFINE_COMPILERRT_PRIVATE_FUNCTION_UNMANGLED(name) \
   .globl name SEPARATOR             \
-  .private_extern name SEPARATOR    \
+  .hidden name SEPARATOR    \
   name:
 
 #endif /* COMPILERRT_ASSEMBLY_H */

lib/libcompiler_rt/Makefile

@@ -6,7 +6,7 @@ LIB=	compiler_rt
 NO_PIC=
 WARNS?=	2
 
-CFLAGS+=${PICFLAG}
+CFLAGS+=${PICFLAG} -fvisibility=hidden -DVISIBILITY_HIDDEN
 
 .if ${MACHINE_CPUARCH} == "amd64"
 CRTARCH=x86_64