PPC/s390: enable gn build on s390x and ppc64le

Bug: 
Change-Id: Iac1ad60e8aa4f5ac3fac9069a2f958cb1449d03c
Reviewed-on: https://chromium-review.googlesource.com/747534
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Leon Scroggins <scroggo@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#513500}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1dc34c0d9553339cb54970c7aadd05aa5c81dd57

tools/gn/substitution_writer.cc

diff --git a/tools/gn/substitution_writer.cc b/tools/gn/substitution_writer.cc
index 50b1e2d..19a4436 100644
--- a/tools/gn/substitution_writer.cc
+++ b/tools/gn/substitution_writer.cc
@@ -584,14 +584,12 @@
       if (target->output_dir().is_null()) {
         return ApplyPatternToLinkerAsOutputFile(
             target, tool, tool->default_output_dir()).value();
-      } else {
-        SetDirOrDotWithNoSlash(RebasePath(
-                target->output_dir().value(),
-                target->settings()->build_settings()->build_dir()),
-            &result);
-        return result;
       }
-      break;
+      SetDirOrDotWithNoSlash(RebasePath(
+              target->output_dir().value(),
+              target->settings()->build_settings()->build_dir()),
+          &result);
+      return result;
 
     case SUBSTITUTION_OUTPUT_EXTENSION:
       // Use the extension provided on the target if specified, otherwise