Now gnu11 is the default, bump experimental to gnu17.

Bug: http://b/232413369
Test: treehugger
Change-Id: I8a2b1eef744c219811c32ad46688437a1ba3f21e
diff --git a/cc/config/global.go b/cc/config/global.go
index 2f00cfa..1c4ad7f 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -281,7 +281,7 @@
 
 	CStdVersion               = "gnu11"
 	CppStdVersion             = "gnu++17"
-	ExperimentalCStdVersion   = "gnu11"
+	ExperimentalCStdVersion   = "gnu17"
 	ExperimentalCppStdVersion = "gnu++2a"
 
 	// prebuilts/clang default settings.