rmlint: fix NIX_* environment propagations to scons

scons build system does not work by default in nixpkgs envoironment as
it filters system environment and throws away NIX_* flags:

    https://scons.org/doc/2.1.0/HTML/scons-user/x1750.html

Fix build system to always propagate os.environment. Drop the
workarounds that pass subset of the variables through.

pkgs/tools/misc/rmlint/default.nix

@@ -31,6 +31,11 @@ stdenv.mkDerivation rec {
     sha256 = "15xfkcw1bkfyf3z8kl23k3rlv702m0h7ghqxvhniynvlwbgh6j2x";
   };
 
+  patches = [
+    # pass through NIX_* environment variables to scons.
+    ./scons-nix-env.patch
+  ];
+
   nativeBuildInputs = [
     pkg-config
     sphinx
@@ -56,9 +61,6 @@ stdenv.mkDerivation rec {
   ];
 
   prePatch = ''
-    export CFLAGS="$NIX_CFLAGS_COMPILE"
-    export LDFLAGS="''${NIX_LDFLAGS//-rpath /-Wl,-rpath=}"
-
     # remove sources of nondeterminism
     substituteInPlace lib/cmdline.c \
       --replace "__DATE__" "\"Jan  1 1970\"" \
@@ -67,6 +69,7 @@ stdenv.mkDerivation rec {
       --replace "gzip -c " "gzip -cn "
   '';
 
+  # Otherwise tries to access /usr.
   prefixKey = "--prefix=";
 
   sconsFlags = lib.optionals (!withGui) [ "--without-gui" ];

pkgs/tools/misc/rmlint/scons-nix-env.patch

@@ -0,0 +1,19 @@
+scons does not use os environment by default:
+  https://scons.org/doc/2.1.0/HTML/scons-user/x1750.html
+
+nixpkgs' cc-wrapper on the other hand relies on various NIX_* variables
+to be passed through like NIX_CFLAGS_COMPILE_BEFORE.
+--- a/SConstruct
++++ b/SConstruct
+@@ -559,10 +559,7 @@ options = dict(
+     SHLINKCOMSTR=link_shared_library_message,
+     LINKCOMSTR=link_program_message,
+     PREFIX=GetOption('prefix'),
+-    ENV = dict([ (key, os.environ[key])
+-                 for key in os.environ
+-                 if key in ['PATH', 'TERM', 'HOME', 'PKG_CONFIG_PATH']
+-              ])
++    ENV = os.environ,
+ )
+ 
+ if ARGUMENTS.get('VERBOSE') == "1":