Fix for MinGW build on Windows

GG_LONGLONG and GG_ULONGLONG shall use LL and ULL suffixes,
since MinGW is actuall a GCC compiler.

Solved by checking whether compilation happens with MinGW
or not using standard MinGW's __MINGW32__ and __MINGW64__
definitions.

Change-Id: I789b34f6342a56ba42f4b280f7242700022ab7a1

internal/ceres/collections_port.h

diff --git a/internal/ceres/collections_port.h b/internal/ceres/collections_port.h
index 063b6d3..715c975 100644
--- a/internal/ceres/collections_port.h
+++ b/internal/ceres/collections_port.h
@@ -77,7 +77,7 @@
 template<typename K>
 struct HashSet : std::tr1::unordered_set<K> {};
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW64__) && !defined(__MINGW32__)
 #define GG_LONGLONG(x) x##I64
 #define GG_ULONGLONG(x) x##UI64
 #else