gcc: fix build with new SDK pattern

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

@@ -7,13 +7,6 @@
 let
   forceLibgccToBuildCrtStuff =
     import ./libgcc-buildstuff.nix { inherit lib stdenv; };
-
-  # todo(@reckenrode) Remove in staging. This is ugly, but it avoid unwanted rebuilds on Darwin and Linux.
-  enableDarwinFixesForStagingNext =
-    version:
-    stdenv.buildPlatform.isDarwin
-    && stdenv.buildPlatform.isx86_64
-    && lib.versionOlder version "10";
 in
 
 originalAttrs: (stdenv.mkDerivation (finalAttrs: originalAttrs // {
@@ -27,20 +20,11 @@ originalAttrs: (stdenv.mkDerivation (finalAttrs: originalAttrs // {
 
     if test "$staticCompiler" = "1"; then
         EXTRA_LDFLAGS="-static"
-    ${
-      if enableDarwinFixesForStagingNext finalAttrs.version then
-        ''
-          elif test "''${NIX_DONT_SET_RPATH-}" != "1"; then
-              EXTRA_LDFLAGS="-Wl,-rpath,''${!outputLib}/lib"
-          else
-              EXTRA_LDFLAGS=""
-        ''
-      else
-        ''
-          else
-              EXTRA_LDFLAGS="-Wl,-rpath,''${!outputLib}/lib"
-        ''
-    }fi
+    elif test "''${NIX_DONT_SET_RPATH-}" != "1"; then
+        EXTRA_LDFLAGS="-Wl,-rpath,''${!outputLib}/lib"
+    else
+        EXTRA_LDFLAGS=""
+    fi
 
     # GCC interprets empty paths as ".", which we don't want.
     if test -z "''${CPATH-}"; then unset CPATH; fi
@@ -74,24 +58,14 @@ originalAttrs: (stdenv.mkDerivation (finalAttrs: originalAttrs // {
                 extraLDFlags=("-L/usr/lib64" "-L/usr/lib")
                 libc_libdir="/usr/lib"
             fi
-            ${
-              if enableDarwinFixesForStagingNext finalAttrs.version then
-                ''
-                  extraLDFlags=("-L$libc_libdir")
-                          nixDontSetRpathVar=NIX_DONT_SET_RPATH''${post}
-                          if test "''${!nixDontSetRpathVar-}" != "1"; then
-                              extraLDFlags+=("-rpath" "$libc_libdir")
-                          fi
-                          extraLDFlags+=("''${extraLDFlags[@]}")
-                ''
-              else
-                ''
-                  extraLDFlags=("-L$libc_libdir" "-rpath" "$libc_libdir"
-                                        "''${extraLDFlags[@]}")
-                ''
-# The strange indentation with the next line is to ensure the string renders the same when the condition is false,
-# which is necessary to prevent unwanted rebuilds in staging-next.
-}        for i in "''${extraLDFlags[@]}"; do
+            declare -a prefixExtraLDFlags=()
+            prefixExtraLDFlags=("-L$libc_libdir")
+            nixDontSetRpathVar=NIX_DONT_SET_RPATH''${post}
+            if test "''${!nixDontSetRpathVar-}" != "1"; then
+                prefixExtraLDFlags+=("-rpath" "$libc_libdir")
+            fi
+            extraLDFlags=("''${prefixExtraLDFlags[@]}" "''${extraLDFlags[@]}")
+            for i in "''${extraLDFlags[@]}"; do
                 declare -g EXTRA_LDFLAGS''${post}+=" -Wl,$i"
             done
         done

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

@@ -5,7 +5,7 @@
 , threadsCross
 , version
 
-, binutils, gmp, mpfr, libmpc, isl
+, apple-sdk, binutils, gmp, mpfr, libmpc, isl
 
 , enableLTO
 , enableMultilib
@@ -112,7 +112,11 @@ let
     ]
     ++ lib.optionals (!withoutTargetLibc) [
       (if libcCross == null
-       then "--with-native-system-header-dir=${lib.getDev stdenv.cc.libc}/include"
+       then (
+        # GCC will search for the headers relative to SDKROOT on Darwin, so it will find them in the store.
+        if targetPlatform.isDarwin then "--with-native-system-header-dir=/usr/include"
+        else "--with-native-system-header-dir=${lib.getDev stdenv.cc.libc}/include"
+       )
        else "--with-native-system-header-dir=${lib.getDev libcCross}${libcCross.incdir or "/include"}")
       # gcc builds for cross-compilers (build != host) or cross-built
       # gcc (host != target) always apply the offset prefix to disentangle
@@ -132,7 +136,8 @@ let
       #
       # We pick "/" path to effectively avoid sysroot offset and make it work
       # as a native case.
-      "--with-build-sysroot=/"
+      # Darwin requires using the SDK as the sysroot for `SDKROOT` to work correctly.
+      "--with-build-sysroot=${if targetPlatform.isDarwin then apple-sdk.sdkroot else "/"}"
       # Same with the stdlibc++ headers embedded in the gcc output
       "--with-gxx-include-dir=${placeholder "out"}/include/c++/${version}/"
     ]

pkgs/development/compilers/gcc/default.nix

@@ -34,6 +34,7 @@
 , nukeReferences
 , callPackage
 , majorMinorVersion
+, apple-sdk
 , cctools
 , darwin
 }:
@@ -105,6 +106,7 @@ let
       ;
       # inherit generated with 'nix eval --json --impure --expr "with import ./. {}; lib.attrNames (lib.functionArgs gcc${majorVersion}.cc.override)" | jq '.[]' --raw-output'
       inherit
+        apple-sdk
         binutils
         buildPackages
         cargo