Add implicit null pointer and stack overflow checks for Mips.

(cherry picked from commit 22bb5a2ebc1e2724179faf4660b2735dcb185f21)

Bug: 21555893
Change-Id: I2a995be128a5603d08753c14956dd8c8240ac63c
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 6c55129..1453e9f 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -921,6 +921,8 @@
     case kX86:
     case kArm64:
     case kX86_64:
+    case kMips:
+    case kMips64:
       implicit_null_checks_ = true;
       // Installing stack protection does not play well with valgrind.
       implicit_so_checks_ = (RUNNING_ON_VALGRIND == 0);