treewide: Get rid of -dumpmachine in favor of static info

pkgs/applications/networking/browsers/firefox/common.nix

@@ -180,7 +180,7 @@ stdenv.mkDerivation ({
       $(< ${stdenv.cc}/nix-support/cc-cflags) \
       ${stdenv.cc.default_cxx_stdlib_compile} \
       ${lib.optionalString stdenv.cc.isClang "-idirafter ${stdenv.cc.cc}/lib/clang/${lib.getVersion stdenv.cc.cc}/include"} \
-      ${lib.optionalString stdenv.cc.isGNU "-isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc} -isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc}/$(cc -dumpmachine)"} \
+      ${lib.optionalString stdenv.cc.isGNU "-isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc} -isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc}/${stdenv.hostPlatform.config}"} \
       $NIX_CFLAGS_COMPILE"
 
     echo "ac_add_options BINDGEN_CFLAGS='$BINDGEN_CFLAGS'" >> $MOZCONFIG

pkgs/applications/networking/mailreaders/thunderbird/default.nix

@@ -191,7 +191,7 @@ stdenv.mkDerivation rec {
           lib.getVersion stdenv.cc.cc
         } -isystem ${stdenv.cc.cc}/include/c++/${
           lib.getVersion stdenv.cc.cc
-        }/$(cc -dumpmachine)"
+        }/${stdenv.hostPlatform.config}"
       } \
       $NIX_CFLAGS_COMPILE"
 

pkgs/build-support/cc-wrapper/default.nix

@@ -48,7 +48,7 @@ let
   coreutils_bin = if nativeTools then "" else getBin coreutils;
 
   default_cxx_stdlib_compile = if (targetPlatform.isLinux && !(cc.isGNU or false) && !nativeTools && cc ? gcc) && !(targetPlatform.useLLVM or false) then
-    "-isystem $(echo -n ${cc.gcc}/include/c++/*) -isystem $(echo -n ${cc.gcc}/include/c++/*)/$(${cc.gcc}/bin/gcc -dumpmachine)"
+    "-isystem $(echo -n ${cc.gcc}/include/c++/*) -isystem $(echo -n ${cc.gcc}/include/c++/*)/${targetPlatform.config}"
   else if targetPlatform.isDarwin && (libcxx != null) && (cc.isClang or false) && !(targetPlatform.useLLVM or false) then
     "-isystem ${libcxx}/include/c++/v1"
   else "";