Revert "Move system/core/include from -isystem to -I"

This reverts commit e4bba1e8358043491e99d74e3757cd2c6dce3702.

Bug: 31492149
Change-Id: If46d240274f1a59ac36579157c575b54f2ffd58f
diff --git a/cc/config/global.go b/cc/config/global.go
index d17a7d1..5b49bc3 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -93,11 +93,10 @@
 	// Everything in these lists is a crime against abstraction and dependency tracking.
 	// Do not add anything to this list.
 	pctx.PrefixedPathsForOptionalSourceVariable("CommonGlobalIncludes", "-I",
-		[]string{
-			"system/core/include",
-		})
+		[]string{})
 	pctx.PrefixedPathsForOptionalSourceVariable("CommonGlobalSystemIncludes", "-isystem ",
 		[]string{
+			"system/core/include",
 			"system/media/audio/include",
 			"hardware/libhardware/include",
 			"hardware/libhardware_legacy/include",