[CMake] cmake shared library exported symbols on 64bit AIX XLC compiler

[Michael Hufer]

Hi,
we have issues linking against shared libraries created  in our project 
on AIX
7.1 with XLC 12.1 when creating 64bit applications. The created shared
libraries to not export any symbols.
After some digging around I figured out that this is due to a missing 
argument
for IBM's XL CreateExportList tool called from the generated "link.txt" 
file.
For 64bit shared libraries this tool should be called with -X64 (and 
-X32 for 32bit to be consistent).

The arguments for this tool seems to be set in "Modules/Compiler/XL.cmake".
Unfortunately I could not figure out myself how to add or not add the "-X64"
to the commandline, depending on the whether a particular build run is
creating 32 or 64bit objects.
Could someone with more intimate knowledge of how the CMake internal 
modules handle this look into this, please?

Thanks,

-- 
Michael Hufer
Senior Software Developer
-------------------------------
Dion Global Solutions GmbH
Mainzer Landstr. 199  I  60322 Frankfurt am Main  I  Germany
phone: +49 69 50952 241
email:michael.hufer at dionglobal.com | web: www.dionglobal.com/de
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Geschäftsführer / Managing Directors: Ralph James Horne, Joseph Nash