IRSL: Fix check of path to Intel redistdir

Fix a cut-n-paste error from commit fd4406f3 (IRSL: Add Intel compiler
support, 2017-08-16, v3.10.0-rc1~187^2).  Make the checked and used
paths match.

Modules/InstallRequiredSystemLibraries.cmake

@@ -87,7 +87,7 @@ foreach(LANG IN ITEMS C CXX Fortran)
       elseif(APPLE)
         get_filename_component(_Intel_redistdir "${_Intel_basedir}/../../compiler/lib" ABSOLUTE)
       else()
-        if(EXISTS "${_Intel_basedir}/../lib/${_Intel_archdir}_lin")
+        if(EXISTS "${_Intel_basedir}/../lib/${_Intel_archdir}")
           get_filename_component(_Intel_redistdir "${_Intel_basedir}/../lib/${_Intel_archdir}" ABSOLUTE)
         else()
           get_filename_component(_Intel_redistdir "${_Intel_basedir}/../../compiler/lib/${_Intel_archdir}_lin" ABSOLUTE)