cext: fix warnings when building for py3 on Windows

MSVC++ 14 now has standard int types that don't need to be redefined (I didn't
go back to see when they came along since the build system wants either 2008 or
2015), but doesn't have ssize_t.  The FILE pointer in posixfile is only used on
python2.

mercurial/cext/osutil.c

@@ -1217,7 +1217,9 b' static PyObject *posixfile(PyObject *sel'
 	char fpmode[4];
 	int fppos = 0;
 	int plus;
+#ifndef IS_PY3K
 	FILE *fp;
+#endif
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwds, PY23("et|si:posixfile",
 							  "et|yi:posixfile"),

mercurial/compat.h

@@ -3,6 +3,7 b''
 
 #ifdef _WIN32
 #ifdef _MSC_VER
+#if _MSC_VER < 1900
 /* msvc 6.0 has problems */
 #define inline __inline
 #if defined(_WIN64)
@@ -21,6 +22,18 b' typedef unsigned short uint16_t;'
 typedef unsigned long uint32_t;
 typedef unsigned __int64 uint64_t;
 #else
+/* VC++ 14 */
+#include <stdint.h>
+
+#if defined(_WIN64)
+typedef __int64 ssize_t;
+#else
+typedef int ssize_t;
+#endif
+#endif /* _MSC_VER < 1900 */
+
+#else
+/* not msvc */
 #include <stdint.h>
 #endif
 #else