Suppress some warnings on linux.

R=reed@google.com
Review URL: https://codereview.appspot.com/6572046

git-svn-id: http://skia.googlecode.com/svn/trunk@5687 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/MathTest.cpp b/tests/MathTest.cpp
index 086b737..c0babee 100644
--- a/tests/MathTest.cpp
+++ b/tests/MathTest.cpp
@@ -184,14 +184,14 @@
  */
 static bool equal_float_native_skia(float x, uint32_t ni, uint32_t si) {
     if (!(x == x)) {    // NAN
-        return si == SK_MaxS32 || si == SK_MinS32;
+        return ((int32_t)si) == SK_MaxS32 || ((int32_t)si) == SK_MinS32;
     }
     // for out of range, C is undefined, but skia always should return NaN32
     if (x > SK_MaxS32) {
-        return si == SK_MaxS32;
+        return ((int32_t)si) == SK_MaxS32;
     }
     if (x < -SK_MaxS32) {
-        return si == SK_MinS32;
+        return ((int32_t)si) == SK_MinS32;
     }
     return si == ni;
 }