IBMClang: No thin LTO on AIX

nicolerabjohnrequested to merge
nicolerabjohn/cmake:nicolerabjohn/aixThinLTO into master

AIX does not yet support thin LTO. This checks to see whether the compiler is being run on AIX, and passes flto as opposed to flto=thin if so.

Topic-rename: ibmclang-aix-thin-lto

Edited by Brad King

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