gcc: use gcc8 on darwin

pkgs/development/compilers/gcc/8/default.nix

@@ -373,9 +373,6 @@ stdenv.mkDerivation ({
       stdenv.lib.platforms.freebsd ++
       stdenv.lib.platforms.illumos ++
       stdenv.lib.platforms.darwin;
-
-    # See #40038
-    broken = stdenv.isDarwin;
   };
 }
 

pkgs/top-level/all-packages.nix

@@ -7518,7 +7518,7 @@ in
   gerbil-unstable = callPackage ../development/compilers/gerbil/unstable.nix { stdenv = gccStdenv; };
 
   gccFun = callPackage ../development/compilers/gcc/8;
-  gcc = if stdenv.isDarwin then gcc7 else gcc8;
+  gcc = gcc8;
   gcc-unwrapped = gcc.cc;
 
   gccStdenv = if stdenv.cc.isGNU then stdenv else stdenv.override {