ci: add support for LLVM 15

This commit switches to LLVM 15 everywhere by default, while still
keeping LLVM 14 support.

targets/esp32c3.json

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

targets/fe310.json

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

targets/k210.json

@@ -1,6 +1,6 @@
 {
 	"inherits": ["riscv64"],
-	"features": "+64bit,+a,+c,+d,+f,+m",
+	"features": "+64bit,+a,+c,+d,+f,+m,-relax,-save-restore",
 	"build-tags": ["k210", "kendryte"],
 	"code-model": "medium"
 }

targets/riscv-qemu.json

@@ -1,6 +1,6 @@
 {
 	"inherits": ["riscv32"],
-	"features": "+a,+c,+m",
+	"features": "+a,+c,+m,-relax,-save-restore",
 	"build-tags": ["virt", "qemu"],
 	"default-stack-size": 4096,
 	"linkerscript": "targets/riscv-qemu.ld",