mesa/glthread: fix misaligned address access

mesa/glthread: fix misaligned address access

Address sanitizer reports lot of misaligned access:
SUMMARY: AddressSanitizer: undefined-behavior main/marshal.c:276:31 in
main/marshal.c:276:31: runtime error: load of misaligned address 0x631000104866 for type
'const GLuint' (aka 'const unsigned int'), which requires 4 byte alignment
0x631000104866: note: pointer points here
 92 88 00 00 00 00  00 00 4a 03 0c 00 93 88  00 00 00 00 00 00 02 01  0c 00 40 8d 00 00 00 00  00 00
             ^
SUMMARY: AddressSanitizer: undefined-behavior main/marshal_generated.c:28725:12 in
main/marshal_generated.c:28726:12: runtime error: member access within misaligned address 0x6310003fc874 for type
'struct marshal_cmd_VertexAttribPointer', which requires 8 byte alignment
0x6310003fc874: note: pointer points here
  01 00 00 00 7a 02 20 00  00 00 00 00 be be be be  be be be be be be be be  be be be be be be be be
              ^
SUMMARY: AddressSanitizer: undefined-behavior main/marshal_generated.c:28726:12 in
main/marshal_generated.c:28726:12: runtime error: store to misaligned address 0x6310003fc87c for type
'GLint' (aka 'int'), which requires 8 byte alignment
0x6310003fc87c: note: pointer points here
  00 00 00 00 be be be be  be be be be be be be be  be be be be be be be be  be be be be be be be be

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>