Try /MTd on Debug Windows builds.

The people clamor for it!  I doubt we'll care in our testing.

BUG=skia:5928

Change-Id: I80d3948fd1f5d0b956c308bc3a6183b8660575ae
Reviewed-on: https://skia-review.googlesource.com/7364
Commit-Queue: Mike Klein <mtklein@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index 97e5368..c6d0658 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -386,6 +386,12 @@
   }
 }
 
+config("debug") {
+  if (is_win) {
+    cflags = [ "/MTd" ]
+  }
+}
+
 config("release") {
   if (is_win) {
     cflags = [
diff --git a/gn/BUILDCONFIG.gn b/gn/BUILDCONFIG.gn
index 23e5288..58cfb23 100644
--- a/gn/BUILDCONFIG.gn
+++ b/gn/BUILDCONFIG.gn
@@ -132,7 +132,9 @@
   "//gn:warnings",
   "//gn:warnings_except_public_headers",
 ]
-if (!is_debug) {
+if (is_debug) {
+  default_configs += [ "//gn:debug" ]
+} else {
   default_configs += [ "//gn:release" ]
 }
 if (!is_official_build) {