MIPS64: Fixed int vs. uintptr_t confusion (plus some cleanup on the way).

Port r23966 (a498d5e3)

BUG=
R=jkummerow@chromium.org, paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/570563006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23986 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/cctest/test-platform.cc

@@ -22,6 +22,8 @@ void GetStackPointer(const v8::FunctionCallbackInfo<v8::Value>& args) {
   __asm__ __volatile__("mov x16, sp; str x16, %0" : "=g"(sp_addr));
 #elif V8_HOST_ARCH_MIPS
   __asm__ __volatile__("sw $sp, %0" : "=g"(sp_addr));
+#elif V8_HOST_ARCH_MIPS64
+  __asm__ __volatile__("sd $sp, %0" : "=g"(sp_addr));
 #else
 #error Host architecture was not detected as supported by v8
 #endif