bintools: only add macos flags when targeting macOS

We can’t set this for cross-compiling since we use the GNU linker.
Instead, set these flags only when targetPlatform is macOS.

Fixes #80754

Fixes #83141

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

@@ -248,6 +248,11 @@ stdenv.mkDerivation {
       printWords "''${ldflagsBefore[@]}" > $out/nix-support/libc-ldflags-before
     '')
 
+    + optionalString stdenv.targetPlatform.isMacOS ''
+      # Ensure consistent LC_VERSION_MIN_MACOSX and remove LC_UUID.
+      echo "-macosx_version_min 10.12 -sdk_version 10.12 -no_uuid" >> $out/nix-support/libc-ldflags-before
+    ''
+
     + optionalString (!nativeTools) ''
       ##
       ## User env support

pkgs/stdenv/darwin/default.nix

@@ -36,9 +36,7 @@ in rec {
     export NIX_IGNORE_LD_THROUGH_GCC=1
     export SDKROOT=
 
-    # Ensure consistent LC_VERSION_MIN_MACOSX and remove LC_UUID.
     export MACOSX_DEPLOYMENT_TARGET=${macosVersionMin}
-    export NIX_LDFLAGS+=" -macosx_version_min ${macosVersionMin} -sdk_version ${appleSdkVersion} -no_uuid"
 
     # Workaround for https://openradar.appspot.com/22671534 on 10.11.
     export gl_cv_func_getcwd_abort_bug=no