std.Target: Add muslabin32 and muslabi64 tags to Abi.

Once we upgrade to LLVM 20, these should be lowered verbatim rather than to
simply musl. Similarly, the special case in llvmMachineAbi() should go away.

src/codegen/llvm.zig

@@ -270,6 +270,8 @@ pub fn targetTriple(allocator: Allocator, target: std.Target) ![]const u8 {
         .android => "android",
         .androideabi => "androideabi",
         .musl => "musl",
+        .muslabin32 => "musl", // Should be muslabin32 in LLVM 20.
+        .muslabi64 => "musl", // Should be muslabi64 in LLVM 20.
         .musleabi => "musleabi",
         .musleabihf => "musleabihf",
         .muslx32 => "muslx32",