root: fix build by upstream patch

Also refactor the expression a little.

pkgs/applications/science/misc/root/cmake.patch

@@ -1,5 +1,5 @@
---- cmake/modules/RootBuildOptions.cmake	1969-12-31 20:30:01.000000000 -0330
-+++ cmake/modules/RootBuildOptions.cmake	2014-01-10 14:09:29.424937408 -0330
+--- a/cmake/modules/RootBuildOptions.cmake	1969-12-31 20:30:01.000000000 -0330
++++ b/cmake/modules/RootBuildOptions.cmake	2014-01-10 14:09:29.424937408 -0330
 @@ -149,7 +149,7 @@
  
  #---General Build options----------------------------------------------------------------------

pkgs/applications/science/misc/root/default.nix

@@ -1,4 +1,5 @@
-{ stdenv, fetchurl, cmake, mesa, libX11, gfortran, libXpm, libXft, libXext, zlib }:
+{ stdenv, fetchurl, fetchpatch, cmake, mesa, gfortran
+, libX11,libXpm, libXft, libXext, zlib }:
 
 stdenv.mkDerivation rec {
   name = "root-${version}";
@@ -14,8 +15,15 @@ stdenv.mkDerivation rec {
   # CMAKE_INSTALL_RPATH_USE_LINK_PATH is set to FALSE in
   # <rootsrc>/cmake/modules/RootBuildOptions.cmake.
   # This patch sets it to TRUE.
-  patches = [ ./cmake.patch ];
-  patchFlags = "-p0";
+  patches = [
+    ./cmake.patch
+    (fetchpatch {
+      name = "fix-tm_t-member.diff";
+      url = "https://github.com/root-mirror/root/commit/"
+        + "08b08412bafc24fa635b0fdb832097a3aa2fa1d2.diff";
+      sha256 = "0apbp51pk8471gl06agx3i88dn76p6gpkgf1ssfhcyam0bjl8907";
+    })
+  ];
 
   enableParallelBuilding = true;