Support Win64 pointer-sized types

Since we're generating stub types from khrplatform.h because we can't
include it reliably, we'll have to deal with some of the fallout of the
Win64 types.

Fixes: #246

src/gen_dispatch.py

@@ -515,9 +515,17 @@ def write_header(self, out_file):
             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 long khronos_intptr_t;')
-            self.outln('typedef long khronos_ssize_t;')
-            self.outln('typedef unsigned long khronos_usize_t;')
+            self.outln('#ifdef _WIN64')
+            self.outln('typedef signed   long long int khronos_intptr_t;')
+            self.outln('typedef unsigned long long int khronos_uintptr_t;')
+            self.outln('typedef signed   long long int khronos_ssize_t;')
+            self.outln('typedef unsigned long long int khronos_usize_t;')
+            self.outln('#else')
+            self.outln('typedef signed   long int      khronos_intptr_t;')
+            self.outln('typedef unsigned long int      khronos_uintptr_t;')
+            self.outln('typedef signed   long int      khronos_ssize_t;')
+            self.outln('typedef unsigned long int      khronos_usize_t;')
+            self.outln('#endif')
             self.outln('typedef uint64_t khronos_utime_nanoseconds_t;')
             self.outln('typedef int64_t khronos_stime_nanoseconds_t;')
             self.outln('#define KHRONOS_MAX_ENUM 0x7FFFFFFF')