graphics/opennurbs: fix byte order and pointer size code

• check for the ILP32 macro when determining pointer size. This catches all of our 32 bit platforms
• add some code to test the compiler's own byte order macros to the header that tries to determine the byte order
• remove explicit architecture list in favour of that code

This fixes the build on armv7.

Approved by: portmgr (build fix blanket)
MFH: 2026Q2