ipa-pta.conf workaround for LLVM 15+

[LtdJorge]

Title: sys-devel/llvm: -fipa-pta workaround for LLVM. Fixes #881 although not only does LLVM 16 not compile with it, but at least 15.0.7-r3

The failure happens always while generating code for target devices with TableGen (calls to /var/tmp/portage/sys-devel/llvm-{version}/work/{currently compiling ABI}/bin/llvm-tblgen).