Use -unknown when converting WASI/Emscripten target triples into LLVM triples

The "musl" part of the Zig target triples `wasm32-wasi-musl` and
`wasm32-emscripten-musl` refers to the libc, not really the ABI.

For WASM, most LLVM-based tooling uses `wasm32-wasi`, which is
normalized into `wasm32-unknown-wasi`, with an implicit `-unknown` and
without `-musl`.

Similarly, Emscripten uses `wasm32-unknown-emscripten` without `-musl`.

By using `-unknown` instead of `-musl` we get better compatibility with
external tooling.

src/codegen/llvm.zig

@@ -264,7 +264,12 @@ pub fn targetTriple(allocator: Allocator, target: std.Target) ![]const u8 {
         .eabihf => "eabihf",
         .android => "android",
         .androideabi => "androideabi",
-        .musl => "musl",
+        .musl => switch (target.os.tag) {
+            // For WASI/Emscripten, "musl" refers to the libc, not really the ABI.
+            // "unknown" provides better compatibility with LLVM-based tooling for these targets.
+            .wasi, .emscripten => "unknown",
+            else => "musl",
+        },
         .muslabin32 => "musl", // Should be muslabin32 in LLVM 20.
         .muslabi64 => "musl", // Should be muslabi64 in LLVM 20.
         .musleabi => "musleabi",