llvm: Fix C ABI integer promotion for loongarch64.

It appears to just be a 1:1 copy of riscv64, including the super weird sign
extension quirk for u32.

Contributes to #21671.

Author: alexrp

src/codegen/llvm.zig

@@ -12578,7 +12578,7 @@ fn ccAbiPromoteInt(
             else => null,
         },
         else => switch (target.cpu.arch) {
-            .riscv64 => switch (int_info.bits) {
+            .loongarch64, .riscv64 => switch (int_info.bits) {
                 0...16 => int_info.signedness,
                 32 => .signed, // LLVM always signextends 32 bit ints, unsure if bug.
                 17...31, 33...63 => int_info.signedness,