rustc: disable test-inherit-env

This fails on hydra on x86_64 for unknown reason.

pkgs/development/compilers/rust/default.nix

@@ -16,7 +16,14 @@ in rec {
   rustc = callPackage ./rustc.nix {
     inherit stdenv llvm targets targetPatches targetToolchains rustPlatform version src;
 
-    patches = [ ./patches/net-tcp-disable-tests.patch ./patches/stdsimd-disable-doctest.patch ];
+    patches = [
+      ./patches/net-tcp-disable-tests.patch
+      ./patches/stdsimd-disable-doctest.patch
+      # Fails on hydra - not locally; the exact reason is unknown.
+      # Comments in the test suggest that some non-reproducible environment
+      # variables such $RANDOM can make it fail.
+      ./patches/disable-test-inherit-env.patch
+    ];
 
     forceBundledLLVM = true;
 

pkgs/development/compilers/rust/patches/disable-test-inherit-env.patch

@@ -0,0 +1,10 @@
+--- rustc-1.26.2-src.org/src/libstd/process.rs	2018-06-01 21:40:11.000000000 +0100
++++ rustc-1.26.2-src/src/libstd/process.rs	2018-06-08 07:50:23.023828658 +0100
+@@ -1745,6 +1745,7 @@
+     }
+
+     #[test]
++    #[ignore]
+     fn test_inherit_env() {
+         use env;
+