Pass -I to yasm

external/libvpx needs -I flags to be propagated to yasm, but can't
handle all the other global flags (like -no-exceptions).  Add -I
arguments to YasmFlags as well as GlobalFlags.

Test: mega-device build of external/libvpx
Change-Id: I1607211c34b031fae8ffc1bd558b26019965a696
diff --git a/cc/library.go b/cc/library.go
index e2ec584..86e3269 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -306,7 +306,9 @@
 func (library *libraryDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
 	exportIncludeDirs := library.flagExporter.exportedIncludes(ctx)
 	if len(exportIncludeDirs) > 0 {
-		flags.GlobalFlags = append(flags.GlobalFlags, includeDirsToFlags(exportIncludeDirs))
+		f := includeDirsToFlags(exportIncludeDirs)
+		flags.GlobalFlags = append(flags.GlobalFlags, f)
+		flags.YasmFlags = append(flags.YasmFlags, f)
 	}
 
 	return library.baseCompiler.compilerFlags(ctx, flags)