Add GN buildfile for gfx

Adds libjpeg and some global flags for Ozone from the GYP build.

Improves error messages for mismatched item types I noticed when writing this patch (changes in builder.cc).

BUG=
R=bradnelson@google.com

Review URL: https://codereview.chromium.org/224633002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@263086 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/linux/BUILD.gn

@@ -29,6 +29,10 @@ config("executable_ldconfig") {
   ]
 }
 
+pkg_config("dridrm") {
+  packages = [ "libdrm" ]
+}
+
 config("fontconfig") {
   libs = [ "fontconfig" ]
 }

config/ui.gni

@@ -60,3 +60,4 @@ use_glib = is_linux
 
 use_clipboard_aurax11 = is_linux && use_aura && use_x11
 
+ozone_platform_dri = use_ozone