Add SSL support to the GN build

build/config/linux/pkg_config.gni

Index: build/config/linux/pkg_config.gni
diff --git a/build/config/linux/pkg_config.gni b/build/config/linux/pkg_config.gni
index b91ee6704b3e9801e980d88032fffb62dd8dd041..c6a3099f1eb856da7d0e99f43e0b4f066096929c 100644
--- a/build/config/linux/pkg_config.gni
+++ b/build/config/linux/pkg_config.gni
@@ -17,6 +17,9 @@ import("//build/config/sysroot.gni")
 #     packages = [ "mything1", "mything2" ]
 #     defines = [ "ENABLE_AWESOME" ]
 #   }
+#
+# You can also use "extra args" to filter out results (see pkg-config.py):
+#   extra_args = [ "-v, "foo" ]
 
 template("pkg_config") {
   assert(defined(invoker.packages),
@@ -28,6 +31,11 @@ template("pkg_config") {
     } else {
       args = invoker.packages
     }
+
+    if (defined(invoker.extra_args)) {
+      args += invoker.extra_args
+    }
+
     pkgresult = exec_script("//build/config/linux/pkg-config.py",
                             args, "value")
     include_dirs = pkgresult[0]