cgo: fix default LLVM version to LLVM 14

Without extra flags, we would try to use LLVM 13 for cgo and LLVM 14 for
other things since 873412b43a. That isn't
great. So fix this by only using LLVM 14 in the cgo package.

cgo/libclang_config_llvm13.go

@@ -1,5 +1,5 @@
-//go:build !byollvm && !llvm14
-// +build !byollvm,!llvm14
+//go:build !byollvm && llvm13
+// +build !byollvm,llvm13
 
 package cgo
 

cgo/libclang_config_llvm14.go

@@ -1,5 +1,5 @@
-//go:build !byollvm && llvm14
-// +build !byollvm,llvm14
+//go:build !byollvm && !llvm13
+// +build !byollvm,!llvm13
 
 package cgo