--- configure.ac 2018-03-06 22:45:44.000000000 +0200 +++ configure.ac.o 2018-04-20 22:41:21.563884174 +0300 @@ -157,6 +157,7 @@ PACKAGE_CFLAGS_ISL='-I${prefix}/include' ;; system) + ISL_SRCDIR="$srcdir/isl" PKG_CHECK_MODULES([ISL], [isl]) PACKAGE_CFLAGS_ISL="$ISL_CFLAGS" esac