llvm: wire up the xtensa backend

As of LLVM 22, it can produce assembly and object files. No LLD support,
however, so using it is still a bit of a pain.

src/codegen/llvm.zig

@@ -4818,7 +4818,7 @@ pub fn initializeLLVMTarget(arch: std.Target.Cpu.Arch) void {
                 bindings.LLVMInitializeXtensaTarget();
                 bindings.LLVMInitializeXtensaTargetInfo();
                 bindings.LLVMInitializeXtensaTargetMC();
-                // There is no LLVMInitializeXtensaAsmPrinter function.
+                bindings.LLVMInitializeXtensaAsmPrinter();
                 bindings.LLVMInitializeXtensaAsmParser();
             }
         },

src/codegen/llvm/bindings.zig

@@ -279,6 +279,7 @@ pub extern fn LLVMInitializeSystemZAsmPrinter() void;
 pub extern fn LLVMInitializeWebAssemblyAsmPrinter() void;
 pub extern fn LLVMInitializeX86AsmPrinter() void;
 pub extern fn LLVMInitializeXCoreAsmPrinter() void;
+pub extern fn LLVMInitializeXtensaAsmPrinter() void;
 pub extern fn LLVMInitializeM68kAsmPrinter() void;
 pub extern fn LLVMInitializeVEAsmPrinter() void;
 pub extern fn LLVMInitializeARCAsmPrinter() void;

src/link/Lld.zig

@@ -812,7 +812,8 @@ fn elfLink(lld: *Lld, arena: Allocator) !void {
             target.cpu.arch == .m68k or
             target.cpu.arch.isSPARC() or
             target.cpu.arch == .ve or
-            target.cpu.arch == .xcore))
+            target.cpu.arch == .xcore or
+            target.cpu.arch == .xtensa))
     {
         // In this case we must do a simple file copy
         // here. TODO: think carefully about how we can avoid this redundant operation when doing

src/target.zig

@@ -227,11 +227,11 @@ pub fn hasLlvmSupport(target: *const std.Target, ofmt: std.Target.ObjectFormat)
         .wasm32,
         .wasm64,
         .ve,
+        .xtensa,
         => true,
 
         // LLVM backend exists but can produce neither assembly nor object files.
         .csky,
-        .xtensa,
         => false,
 
         // Third-party LLVM backend exists.

test/llvm_targets.zig

@@ -344,8 +344,8 @@ const targets = [_]std.Target.Query{
 
     .{ .cpu_arch = .xcore, .os_tag = .freestanding, .abi = .none },
 
-    // .{ .cpu_arch = .xtensa, .os_tag = .freestanding, .abi = .none },
-    // .{ .cpu_arch = .xtensa, .os_tag = .linux, .abi = .none },
+    .{ .cpu_arch = .xtensa, .os_tag = .freestanding, .abi = .none },
+    .{ .cpu_arch = .xtensa, .os_tag = .linux, .abi = .none },
 };
 
 pub fn addCases(