Hide various symbols that shouldn't be exposed.

A mangled symbol in libc.so is a symbol that shouldn't be exported
by libc.so.

Change-Id: Id92d1e1968b3d11d111a5d9ef692adb1ac7694a1
diff --git a/libc/bionic/libc_init_common.h b/libc/bionic/libc_init_common.h
index 23ac305..14105f8 100644
--- a/libc/bionic/libc_init_common.h
+++ b/libc/bionic/libc_init_common.h
@@ -50,7 +50,7 @@
 
 #if defined(__cplusplus)
 struct KernelArgumentBlock;
-void __libc_init_common(KernelArgumentBlock& args);
+void __LIBC_HIDDEN__ __libc_init_common(KernelArgumentBlock& args);
 #endif
 
 #endif