Fix for PR4192: fix the definition of int64_t on x86_64 Linux.

Note that I'm guessing that *BSD and Solaris do the same thing as Linux 
here, but it's quite possible I'm wrong; if the following testcase 
gives an error on x86-64 with gcc for any of those operating systems, please
tell me:

#include <stdint.h>

int64_t x; long x;

llvm-svn: 74583
diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index a513cb1..ba7f190 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -41,6 +41,7 @@
   UIntMaxType = UnsignedLongLong;
   IntPtrType = SignedLong;
   WCharType = SignedInt;
+  Int64Type = SignedLongLong;
   FloatFormat = &llvm::APFloat::IEEEsingle;
   DoubleFormat = &llvm::APFloat::IEEEdouble;
   LongDoubleFormat = &llvm::APFloat::IEEEdouble;