Add brillo cflags

Add __BRILLO__ to global cflags when building for a brillo product.

Bug: 26165350
Change-Id: I0100a8821b763075d1873d0d48fd5bd217afb580
diff --git a/cc/cc.go b/cc/cc.go
index b497d66..6315cbf 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -581,6 +581,10 @@
 				fmt.Sprintf("${%sGlobalCflags}", ctx.HostOrDevice()))
 		}
 
+		if Bool(ctx.AConfig().ProductVariables.Brillo) {
+			flags.GlobalFlags = append(flags.GlobalFlags, "-D__BRILLO__")
+		}
+
 		if ctx.Device() {
 			if Bool(c.Properties.Rtti) {
 				flags.CppFlags = append(flags.CppFlags, "-frtti")