Yaakov Selkowitz authored Aug 10, 2014 and Jon Turney committed Apr 21, 2015

As noted in Initialize.c, _XtInherit needs special treatment as it's both called
as a function, and used as a value to compare with.

We need to change this trickery for x86_64, as the symbols are no longer
underscore prefixed, and the address is 64 bits.

We also cannot place the trampoline in the .data section, as it may be marked
no-execute, so we use a special section for it instead.

v2: Uses of XtInherit must also be marked dllimport, so that they do not use a
thunk, but instead indirect via the __imp_XtInherit auto-import. This avoids
problems with an incorrect relocation being calculated in the case where libXt
and a library using it (e.g. libXaw/libXaw3d/libXm/etc.) are loaded more than
2GiB apart from each other.

This is enough to build a working libXt for Cygwin x86_64, because it uses the
LP64 data model.  I believe that more patches are needed for libXt to work
correctly when built for the Windows LLP64 data model.

Signed-off-by: Yaakov Selkowitz <yselkowitz@cygwin.com>
Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>