Sema: Prevent tail calls of std.builtin.returnError().

LLVM 20 started tail-calling it in some of our test cases, resulting in:

    error: AndMyCarIsOutOfGas
    /home/alexrp/Source/ziglang/zig-llvm20/repro.zig:2:5: 0x103ef9d in main (repro)
        return error.TheSkyIsFalling;
        ^
    /home/alexrp/Source/ziglang/zig-llvm20/repro.zig:6:5: 0x103efa5 in main (repro)
        return error.AndMyCarIsOutOfGas;
        ^
    /home/alexrp/Source/ziglang/zig-llvm20/lib/std/start.zig:656:37: 0x103ee83 in posixCallMainAndExit (repro)
                const result = root.main() catch |err| {
                                        ^

instead of the expected:

    error: AndMyCarIsOutOfGas
    /home/alexrp/Source/ziglang/zig-llvm20/repro.zig:2:5: 0x103f00d in main (repro)
        return error.TheSkyIsFalling;
        ^
    /home/alexrp/Source/ziglang/zig-llvm20/repro.zig:6:5: 0x103f015 in main (repro)
        return error.AndMyCarIsOutOfGas;
        ^
    /home/alexrp/Source/ziglang/zig-llvm20/repro.zig:11:9: 0x103f01d in main (repro)
            try bar();
            ^

Author: alexrp

src/Sema.zig

@@ -19226,7 +19226,7 @@ fn retWithErrTracing(
     const return_err_fn = Air.internedToRef(try sema.getBuiltin(src, .returnError));
 
     if (!need_check) {
-        try sema.callBuiltin(block, src, return_err_fn, .never_inline, &.{}, .@"error return");
+        try sema.callBuiltin(block, src, return_err_fn, .never_tail, &.{}, .@"error return");
         _ = try block.addUnOp(ret_tag, operand);
         return;
     }
@@ -19237,7 +19237,7 @@ fn retWithErrTracing(
 
     var else_block = block.makeSubBlock();
     defer else_block.instructions.deinit(gpa);
-    try sema.callBuiltin(&else_block, src, return_err_fn, .never_inline, &.{}, .@"error return");
+    try sema.callBuiltin(&else_block, src, return_err_fn, .never_tail, &.{}, .@"error return");
     _ = try else_block.addUnOp(ret_tag, operand);
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).@"struct".fields.len +