Fixes build with GCC 5 and later.

diff --git a/packages/base/include/HsBase.h b/packages/base/include/HsBase.h
index aa1a7fb..78d5b46 100644
--- a/packages/base/include/HsBase.h
+++ b/packages/base/include/HsBase.h
@@ -217,15 +217,7 @@ StgWord64 stg_integerToWord64 (StgInt sa, StgByteArray /* Really: mp_limb_t* */
    when compiling to native code.
    -------------------------------------------------------------------------- */
 
-#ifndef INLINE
-# if defined(_MSC_VER)
-#  define INLINE extern __inline
-# elif defined(__GNUC__)
-#  define INLINE extern inline
-# else
-#  define INLINE inline
-# endif
-#endif
+#define INLINE inline
 
 INLINE int __hscore_get_errno(void) { return errno; }
 INLINE void __hscore_set_errno(int e) { errno = e; }