GN: Fix flags writing for targets with unsupported PCHs

This fixes an issue that led to empty compiler flags being written
in the unusual case of a target with a PCH in conjunction with a toolchain
that doesn't support PCHs.

BUG=649899

Review-Url: https://codereview.chromium.org/2410253002
Cr-Original-Commit-Position: refs/heads/master@{#424669}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 52de7c17a1f9e4b3a2ed57d41afd131c0f4f8e69

tools/gn/ninja_binary_target_writer.cc

diff --git a/tools/gn/ninja_binary_target_writer.cc b/tools/gn/ninja_binary_target_writer.cc
index da46149..9772b85 100644
--- a/tools/gn/ninja_binary_target_writer.cc
+++ b/tools/gn/ninja_binary_target_writer.cc
@@ -480,6 +480,9 @@
         pch_file.erase(pch_file.length() - 4);
         out_ << " -include " << pch_file;
       }
+    } else {
+      RecursiveTargetConfigStringsToStream(target_, getter,
+                                           flag_escape_options, out_);
     }
   } else {
     RecursiveTargetConfigStringsToStream(target_, getter,