src/gen_dispatch.py: Make Generated Code Build Under C89

...so that the generated code are buildable by pre-2013 Visual Studio.

 The main thing that this does is that we avoid named initializers, but
 instead initialize the structs in old-school C89 way.

 The generated code may not look that robust, but since this is generated
 code, I think this is not that much an issue; when the Khronos registry gets
 updated, all that is needed is that the code gets re-generated, and we have the
 items in the right order.

src/gen_dispatch.py

@@ -659,9 +659,10 @@ class Generator(object):
         assert(offset < 65536)
 
         self.outln('static const uint16_t enum_string_offsets[] = {')
+        self.outln('    -1, /* {0}_provider_terminator, unused */'.format(self.target))
         for human_name in sorted_providers:
             enum = self.provider_enum[human_name]
-            self.outln('    [{0}] = {1},'.format(enum, self.enum_string_offset[human_name]))
+            self.outln('    {1}, /* {0} */'.format(enum, self.enum_string_offset[human_name]))
         self.outln('};')
         self.outln('')
 
@@ -789,7 +790,7 @@ class Generator(object):
 
         self.outln('static struct dispatch_table resolver_table = {')
         for func in self.sorted_functions:
-            self.outln('    .{0} = epoxy_{0}_dispatch_table_rewrite_ptr,'.format(func.wrapped_name))
+            self.outln('    epoxy_{0}_dispatch_table_rewrite_ptr, /* {0} */'.format(func.wrapped_name))
         self.outln('};')
         self.outln('')