iccifort: remove LIBRARY_PATH entries already known to icc et al

[bartoldeman]

This makes it consistent with Intel's own script that don't set
LIBRARY_PATH either (except for aux components such as TBB)

But only do this for iccifort (single installation) so that in a split
installation icc can still find ifort's libraries and vice versa.

[boegel]

Tested with standalone iccifort that is part of intel/2019b and intel/2020.00 + a couple of installation using that iccifort as toolchain, no problems encountered, so good to go in...

Thanks @bartoldeman!

[boegel]

@bartoldeman I think this broke something after all...

The installation of BLAST+-2.9.0-iimpi-2019b.eb is failing for me when the iccifort module is not including the compiler/lib/intel64 subdirectory in $LIBRARY_PATH with:

ld.gold: error: cannot find -liomp5

The problem doesn't occur when the compiler/lib/intel64 path is still being added to $LIBRARY_PATH by the iccifort module...

[boegel]

After taking a closer look, I noticed the failing link command is using gcc rather than the expected icc or mpiicc, so I guess that's the real problem with building BLAST+ with iimpi/2019b, and this change just exposes that problem better...

[boegel]

To avoid a "wisdom of the ancients" situation: gcc was only used to build a small helper utility during the build of BLAST+, and $LIBS (containing -liomp5) was being picked up, which led to the reported cannot find -liomp5` error.

Fixed by unsetting $LIBS, see easybuilders/easybuild-easyconfigs@4c40033