go: apply upstream patch

This should fix the tests almost always failing on Hydra for i686.

pkgs/development/compilers/go/1.12.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, tzdata, iana-etc, runCommand
+{ stdenv, fetchurl, fetchpatch, tzdata, iana-etc, runCommand
 , perl, which, pkgconfig, patch, procps, pcre, cacert, Security, Foundation
 , mailcap, runtimeShell
 , buildPackages, pkgsTargetTarget
@@ -137,6 +137,11 @@ stdenv.mkDerivation rec {
     ./skip-nohup-tests.patch
     # breaks under load: https://github.com/golang/go/issues/25628
     ./skip-test-extra-files-on-386.patch
+    (fetchpatch { # probably included in >= 1.12.10
+      url = "https://github.com/golang/go/commit/aae0b5b0b.diff";
+      name = "TestGcSys-too-much-memory.diff";
+      sha256 = "1bl9d2pl6n99n9g65cq91sygmp1iva5rmrxbprwn4xd0ql36psa8";
+    })
   ];
 
   postPatch = ''