Move frameworks/native/opengl/include from -isystem to -I

-isystem hides all warnings.  The warnings in
frameworks/native/opengl/include have been fixed, move it from
-isystem to -I.

Test: m -j native
Bug: 31751828

Change-Id: If182ab5664e22f0cfd5be8cb1d0309d07dc85ceb
diff --git a/cc/config/global.go b/cc/config/global.go
index 71c0da4..c8b803b 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -108,10 +108,10 @@
 			"hardware/ril/include",
 			"libnativehelper/include",
 			"frameworks/native/include",
+			"frameworks/native/opengl/include",
 		})
 	pctx.PrefixedPathsForOptionalSourceVariable("CommonGlobalSystemIncludes", "-isystem ",
 		[]string{
-			"frameworks/native/opengl/include",
 			"frameworks/av/include",
 			"frameworks/base/include",
 		})