Use the same typedefs as upstream khrplatform.h in a couple cases.

This should avoid any differences we might end up with compared to
system khrplatform.h.

src/gen_dispatch.py

@@ -501,8 +501,8 @@ class Generator(object):
             self.outln('typedef uint32_t khronos_uint32_t;')
             self.outln('typedef uint64_t khronos_uint64_t;')
             self.outln('typedef float khronos_float_t;')
-            self.outln('typedef intptr_t khronos_intptr_t;')
+            self.outln('typedef long khronos_intptr_t;')
-            self.outln('typedef ptrdiff_t khronos_ssize_t;')
+            self.outln('typedef long khronos_ssize_t;')
             self.outln('typedef unsigned long khronos_usize_t;')
             self.outln('typedef uint64_t khronos_utime_nanoseconds_t;')
             self.outln('typedef int64_t khronos_stime_nanoseconds_t;')