Bug 871783 - Do not copy the stack pointer for alignment checks. r=nbp

Test the stack pointer directly instead of copying it to
a temporary register. This is debug-only code, but tidiness is nice.

js/src/ion/x64/MacroAssembler-x64.cpp

@@ -120,8 +120,7 @@ MacroAssemblerX64::callWithABIPre(uint32_t *stackAdjust)
 #ifdef DEBUG
     {
         Label good;
-        movl(rsp, rax);
-        testq(rax, Imm32(StackAlignment - 1));
+        testq(rsp, Imm32(StackAlignment - 1));
         j(Equal, &good);
         breakpoint();
         bind(&good);

js/src/ion/x86/MacroAssembler-x86.cpp

@@ -149,8 +149,7 @@ MacroAssemblerX86::callWithABIPre(uint32_t *stackAdjust)
     {
         // Check call alignment.
         Label good;
-        movl(esp, eax);
-        testl(eax, Imm32(StackAlignment - 1));
+        testl(esp, Imm32(StackAlignment - 1));
         j(Equal, &good);
         breakpoint();
         bind(&good);