Bug 1906777 - [riscv64]Keep unsigned 32-bit parameter sign-extended in register. r=nika DONTBUILD

On riscv64, 32-bit value in 64-bit register should be sign-extended, even
when it's type is unsigned.

Differential Revision: https://phabricator.services.mozilla.com/D215989

xpcom/reflect/xptcall/md/unix/xptcinvoke_riscv64.cpp

@@ -48,7 +48,9 @@ extern "C" void invoke_copy_to_stack(uint64_t* gpregs, double* fpregs,
           value = s->val.u16;
           break;
         case nsXPTType::T_U32:
-          value = s->val.u32;
+          // On RISC-V, 32-bit values need to be sign-extended in 64-bit
+          // registers, so use the signed value here.
+          value = s->val.i32;
           break;
         case nsXPTType::T_U64:
           value = s->val.u64;