gcc: provide build support for gccrs

Patches from the gccrs project are being upstreamed into gcc. With
these changes we are now able to build a gcc with rust support like
this:

```nix
wrapCC (gcc14.cc.override {
  langRust = true;
});
```

More info:

https://rust-gcc.github.io/

https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608387.html

pkgs/development/compilers/gcc/common/configure-flags.nix

@@ -24,6 +24,7 @@
 , langObjC
 , langObjCpp
 , langJit
+, langRust ? false
 , disableBootstrap ? stdenv.targetPlatform != stdenv.hostPlatform
 }:
 
@@ -171,6 +172,7 @@ let
           ++ lib.optional langObjCpp   "obj-c++"
           ++ lib.optionals crossDarwin [ "objc" "obj-c++" ]
           ++ lib.optional langJit      "jit"
+          ++ lib.optional langRust     "rust"
           )
       }"
     ]

pkgs/development/compilers/gcc/common/dependencies.nix

@@ -31,6 +31,8 @@
 , javaAwtGtk ? false
 , langAda ? false
 , langGo ? false
+, langRust ? false
+, cargo
 , withoutTargetLibc ? null
 , threadsCross ? null
 }:
@@ -53,6 +55,7 @@ in
   ++ optionals javaAwtGtk [ pkg-config ]
   ++ optionals (with stdenv.targetPlatform; isVc4 || isRedox && flex != null) [ flex ]
   ++ optionals langAda [ gnat-bootstrap ]
+  ++ optionals langRust [ cargo ]
   # The builder relies on GNU sed (for instance, Darwin's `sed' fails with
   # "-i may not be used with stdin"), and `stdenvNative' doesn't provide it.
   ++ optionals buildPlatform.isDarwin [ gnused ]

pkgs/development/compilers/gcc/default.nix

@@ -8,6 +8,8 @@
 , reproducibleBuild ? true
 , profiledCompiler ? false
 , langJit ? false
+, langRust ? false
+, cargo
 , staticCompiler ? false
 , enableShared ? stdenv.targetPlatform.hasSharedLibraries
 , enableLTO ? stdenv.hostPlatform.hasSharedLibraries
@@ -128,6 +130,7 @@ let
       inherit
         binutils
         buildPackages
+        cargo
         cloog
         withoutTargetLibc
         darwin
@@ -153,6 +156,7 @@ let
         langJit
         langObjC
         langObjCpp
+        langRust
         lib
         libcCross
         libmpc