set/get_gs hack similar to set/get_fs hack

Implement for GS a similar hack as for FS
This generalises the 0x60 hack that was done for Darwin.
FS_ZERO and GS_0x60 have been renames FS_CONST and GS_CONST,
as in fact these hacks are working with whatever value of FS/GS, as
long as these are not modified

(cherry-picked from: https://bugs.kde.org/show_bug.cgi?id=197259#c14)
Bug: 18597541

Change-Id: Ib29c3b2b2d012e929759b7b17bb30059a5d77174
10 files changed