https://bugs.gentoo.org/659732
https://github.com/libunwind/libunwind/issues/58

From a1437a3d27924e17d00021df3cc659bd998e8580 Mon Sep 17 00:00:00 2001
From: Dave Watson <davejwatson@fb.com>
Date: Thu, 28 Dec 2017 08:26:42 -0800
Subject: [PATCH] Remove PROTECTED visibility

This only works on bfd ld, not lld or gold.
--- a/include/compiler.h
+++ b/include/compiler.h
@@ -43 +43 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
-#  define PROTECTED     __attribute__((visibility ("protected")))
+#  define PROTECTED