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/esp32c3.json

@@ -1,6 +1,6 @@
 {
 	"inherits": ["riscv32"],
-	"features": "+c,+m,-relax,-save-restore",
+	"features": "+c,+m",
 	"build-tags": ["esp32c3", "esp"],
 	"serial": "uart",
 	"rtlib": "compiler-rt",