Only build //build/config/mac:sdk_inputs on Mac.

Bug: 1157103
Change-Id: Ie792de078f7d33cc269eeb489d1381d267d1a681
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2585789Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836244}

build/config/mac/BUILD.gn

@@ -117,7 +117,7 @@ config("strip_all") {
 #
 # The symbolic link for $mac_sdk_path is set up by
 # //build/config/mac/sdk_info.py in //build/config/mac/mac_sdk.gni.
-if (use_system_xcode && use_goma) {
+if (use_system_xcode && use_goma && target_os == "mac") {
   action("sdk_inputs") {
     script = "//build/noop.py"
     outputs = [