all: update to LLVM 14

Switch over to LLVM 14 for static builds. Keep using LLVM 13 for regular
builds for now.

This uses a branch of the upstream Espressif branch to fix an issue,
see: https://github.com/espressif/llvm-project/pull/59

targets/fe310.json

@@ -1,6 +1,6 @@
 {
 	"inherits": ["riscv32"],
 	"cpu": "sifive-e31",
-	"features": "+a,+c,+m,-64bit,-relax,-save-restore",
+	"features": "+a,+c,+m",
 	"build-tags": ["fe310", "sifive"]
 }