fix unittest on platforms with unsigned chars (e.g. linux-ppc)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77471 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/ADT/TwineTest.cpp b/unittests/ADT/TwineTest.cpp
index dae5fa0..2f87476 100644
--- a/unittests/ADT/TwineTest.cpp
+++ b/unittests/ADT/TwineTest.cpp
@@ -36,7 +36,7 @@
   EXPECT_EQ("123", Twine::utostr(123).str());
   EXPECT_EQ("-123", Twine::itostr(-123).str());
   EXPECT_EQ("123", Twine::utostr((char) 123).str());
-  EXPECT_EQ("-123", Twine::itostr((char) -123).str());
+  EXPECT_EQ("-123", Twine::itostr((signed char) -123).str());
 
   EXPECT_EQ("7B", Twine::utohexstr(123).str());
   EXPECT_EQ("FFFFFFFFFFFFFF85", Twine::itohexstr(-123).str());