gcc: use upstream patch

Library/Formula/gcc.rb

@@ -71,9 +71,9 @@ class Gcc < Formula
   # This patch fixes the build on PPC
   # https://gcc.gnu.org/ml/gcc-testresults/2017-01/msg02971.html
   # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80865
-  patch :p0 do
-    url "https://raw.githubusercontent.com/macports/macports-ports/master/lang/gcc7/files/patch-darwin-ppc-2017-01-msg02971.diff"
-    sha256 "98dfb57c9d08430c9656b2afa8967937c3f146b9bb21ac79129ac1cb2c9a4642"
+  patch do
+    url "https://gist.githubusercontent.com/mistydemeo/d35fcc040587cc75bd24d3464e93a45d/raw/c5fe1f0c6393526ff45803b0fc14e028149a245e/gcc_altivec.patch"
+    sha256 "09a795d013ec3e96107bfb9d5c6bba821cc867b88c3bce494ae1564bfd4ababd"
   end
 
   def install