[GN]: Include asmflags in ConfigValues::AppendValues

This ensures that any subconfig asmflags values apply to a config that
references it.

BUG=none
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/1376733005

Cr-Original-Commit-Position: refs/heads/master@{#351583}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1437d0fd62fe019f3cb9f663f81da5d4233e1044

tools/gn/config_values.cc

diff --git a/tools/gn/config_values.cc b/tools/gn/config_values.cc
index d87ed84..73486cd 100644
--- a/tools/gn/config_values.cc
+++ b/tools/gn/config_values.cc
@@ -23,6 +23,7 @@
 }
 
 void ConfigValues::AppendValues(const ConfigValues& append) {
+  VectorAppend(&asmflags_,     append.asmflags_);
   VectorAppend(&cflags_,       append.cflags_);
   VectorAppend(&cflags_c_,     append.cflags_c_);
   VectorAppend(&cflags_cc_,    append.cflags_cc_);