fix pkgconfig handling in cmake

when IGC_DIR is not defined we shouldn't override paths because
/lib/pkgconfig may exists in some distributions.

Change-Id: I843b033ff6b0d91cb866b7ab36fa82a02ca7448e
Signed-off-by: Artur Harasimiuk <artur.harasimiuk@intel.com>

Author: ArturHarasimiuk

CMakeLists.txt

@@ -200,18 +200,18 @@ if(NOT IGC__IGC_TARGETS)
     if(UNIX)
         # on Unix-like use pkg-config
         find_package(PkgConfig)
-        if(IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
+        if(DEFINED IGC_DIR AND IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
             set(ENV{PKG_CONFIG_PATH} "${IGC_DIR}/lib/pkgconfig/")
         endif()
         pkg_check_modules(IGDRCL__IGC igc-opencl)
-        if(IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
+        if(DEFINED IGC_DIR AND IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
             unset(ENV{PKG_CONFIG_PATH})
             set(IGDRCL__IGC_LIBRARY_PATH "${IGC_DIR}/lib/")
             set(ENV{LD_LIBRARY_PATH} "${IGDRCL__IGC_LIBRARY_PATH}")
         endif()
 
         if(IGDRCL__IGC_FOUND)
-            if(IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
+            if(DEFINED IGC_DIR AND IS_DIRECTORY "${IGC_DIR}/lib/pkgconfig/")
                 string(REPLACE "${IGDRCL__IGC_INCLUDEDIR}" "${IGC_DIR}/include/igc" IGDRCL__IGC_INCLUDE_DIRS "${IGDRCL__IGC_INCLUDE_DIRS}")
             endif()