all: add initial LLVM 17 support

This allows us to test and use LLVM 17, now that it is available in
Homebrew.

Full support for LLVM 17 (including using it by default) will have to
wait until Espressif rebases their Xtensa fork of LLVM.

cgo/libclang_config_llvm16.go

@@ -1,8 +1,8 @@
-//go:build !byollvm && !llvm15
+//go:build !byollvm && !llvm15 && !llvm17
 
 package cgo
 
-// As of 2023-05-05, there is a packaging issue on Debian:
+// As of 2023-05-05, there is a packaging issue with LLVM 16 on Debian:
 // https://github.com/llvm/llvm-project/issues/62199
 // A workaround is to fix this locally, using something like this:
 //

cgo/libclang_config_llvm17.go

@@ -0,0 +1,15 @@
+//go:build !byollvm && llvm17
+
+package cgo
+
+/*
+#cgo linux        CFLAGS:  -I/usr/include/llvm-17 -I/usr/include/llvm-c-17 -I/usr/lib/llvm-17/include
+#cgo darwin,amd64 CFLAGS:  -I/usr/local/opt/llvm@17/include
+#cgo darwin,arm64 CFLAGS:  -I/opt/homebrew/opt/llvm@17/include
+#cgo freebsd      CFLAGS:  -I/usr/local/llvm17/include
+#cgo linux        LDFLAGS: -L/usr/lib/llvm-17/lib -lclang
+#cgo darwin,amd64 LDFLAGS: -L/usr/local/opt/llvm@17/lib -lclang -lffi
+#cgo darwin,arm64 LDFLAGS: -L/opt/homebrew/opt/llvm@17/lib -lclang -lffi
+#cgo freebsd      LDFLAGS: -L/usr/local/llvm17/lib -lclang
+*/
+import "C"