Consolidate -std flags

Define the default -std values in global.go, export them in makevars.go,
and use them in compiler.go.

Test: builds
Change-Id: Ia2ae01f63e182d0ad7f371e6d32184bff35a8897
diff --git a/cc/config/global.go b/cc/config/global.go
index 9b77662..348c586 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -37,9 +37,7 @@
 		"-UDEBUG",
 	}
 
-	commonGlobalConlyflags = []string{
-		"-std=gnu99",
-	}
+	commonGlobalConlyflags = []string{}
 
 	deviceGlobalCflags = []string{
 		"-fdiagnostics-color",
@@ -66,6 +64,10 @@
 	IllegalFlags = []string{
 		"-w",
 	}
+
+	CStdVersion      = "gnu99"
+	CppStdVersion    = "gnu++14"
+	GccCppStdVersion = "gnu++11"
 )
 
 var pctx = android.NewPackageContext("android/soong/cc/config")