gildas: fix architecture detection for aarch64

pkgs/applications/science/astronomy/gildas/aarch64.patch

@@ -0,0 +1,12 @@
+diff -ruN gildas-src-jul18a/admin/define-system.sh gildas-src-jul18a.aarch64/admin/define-system.sh
+--- gildas-src-jul18a/admin/define-system.sh	2018-06-12 15:22:32.000000000 +0200
++++ gildas-src-jul18a.aarch64/admin/define-system.sh	2018-07-21 13:05:52.000000000 +0200
+@@ -174,7 +174,7 @@
+     DEFAULT_CONFIG=          # Default config is empty
+     case `uname` in
+         Linux)
+-            if [ `uname -m | grep -c "x86_64"` -ne 0 ]; then
++            if [ `uname -m | grep -c "64"` -ne 0 ]; then
+         	GAG_MACHINE=x86_64
+             else
+         	GAG_MACHINE=pc

pkgs/applications/science/astronomy/gildas/default.nix

@@ -22,7 +22,7 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ gtk2-x11 lesstif cfitsio python27Env ];
 
-  patches = [ ./wrapper.patch ./return-error-code.patch ./clang.patch ./mod.patch ];
+  patches = [ ./wrapper.patch ./return-error-code.patch ./clang.patch ./mod.patch ./aarch64.patch ];
 
   configurePhase=''
     substituteInPlace admin/wrapper.sh --replace '%%OUT%%' $out