This patch adds an option to build against a version of libisl already
installed on the system. The installation is autodetected using the
pkg-config file shipped with isl.
The detection of the library is in the FindISL.cmake module that creates
an imported target.
Contributed-by: Philip Pfaffe <philip.pfaffe@gmail.com>
Differential Revision: https://reviews.llvm.org/D30043
llvm-svn: 296361
Michael Kruse