Move system/media/audio/include from -isystem to -I

-isystem hides all warnings.  The warnings in system/media/audio/include
have been cleaned up, so move it from -isystem to -I.

Test: m -j
Bug: 31997134
Change-Id: I1c0b68935d643992dd9fc7f76583bed286e49325
diff --git a/cc/config/global.go b/cc/config/global.go
index ae43301..ffd9d80 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -95,11 +95,11 @@
 	pctx.PrefixedPathsForOptionalSourceVariable("CommonGlobalIncludes", "-I",
 		[]string{
 			"system/core/include",
+			"system/media/audio/include",
 			"frameworks/native/include",
 		})
 	pctx.PrefixedPathsForOptionalSourceVariable("CommonGlobalSystemIncludes", "-isystem ",
 		[]string{
-			"system/media/audio/include",
 			"hardware/libhardware/include",
 			"hardware/libhardware_legacy/include",
 			"hardware/ril/include",