Revert "main/gcc6: delete in favor of Alpine's gcc6"

This reverts commit d56a2facfb
and changes the main/gcc6 pkgrel to 9999, so it will always be higher
than Alpine's version.

main/gcc6/204-linux_libc_has_function.patch

@@ -0,0 +1,25 @@
+From edec78452d693fb524daa9a6efd45c850b27b25c Mon Sep 17 00:00:00 2001
+From: Szabolcs Nagy <nsz@port70.net>
+Date: Fri, 6 Nov 2015 23:59:20 +0000
+Subject: [PATCH 4/6] linux_libc_has_function
+
+---
+ gcc/config/linux.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/gcc/config/linux.c b/gcc/config/linux.c
+index 250296b..16c3768 100644
+--- a/gcc/config/linux.c
++++ b/gcc/config/linux.c
+@@ -26,7 +26,7 @@ along with GCC; see the file COPYING3.  If not see
+ bool
+ linux_libc_has_function (enum function_class fn_class)
+ {
+-  if (OPTION_GLIBC)
++  if (OPTION_GLIBC || OPTION_MUSL)
+     return true;
+   if (OPTION_BIONIC)
+     if (fn_class == function_c94
+-- 
+2.8.1
+