Fix GLExt for x86_64

Original Reporter info from Mantis: Michalis @michaliskambi

• Reporter name: Michalis Kamburelis

Description:

glext_ExtensionSupported in GLExt unit does arithmetic on pointers casting them to Integer type, this obviously causes Access violations/segfaults from any Load_xxx function when on x86_64.

Fix is to use PtrUInt type. Simple patch is attached.

While I was at it, also GLintptr and GLsizeiptr need fixing (were Integer, should be PtrInt (signed are OK here, looking at how they are supposed to be used in GL)).

Mantis conversion info:

• Mantis ID: 10508
• OS: Debian
• OS Build: testing
• Platform: x86_64
• Version: 2.3.1
• Fixed in version: 2.2.2
• Fixed in revision: 9762 (#23b62be0)