[Polly][CMake] Exclude isl_config from the polly-check-format target.

[philip.pfaffe]

Summary

The custom polly-check-format target runs clang-format over all source files in the directory tree excluding lib/External. isl_config.h is a header file that is generated by CMake in the build directory, and it's not correctly formatted (which I also wouldn't consider necessary, as it is a generated file).

If the build directory is actually inside the Polly source directory (which it might be if you're building Polly out-of-tree), that check always fails. Hence this patch excludes this file from the check-format target.

[grosser]

LGTM

CMakeLists.txt

 # TODO: docs.
 
 
 configure_file( ${CMAKE_CURRENT_SOURCE_DIR}/include/polly/Config/config.h.cmake
                 ${POLLY_BINARY_DIR}/include/polly/Config/config.h )
 
 # Add target to check formatting of polly files
 file( GLOB_RECURSE files *.h lib/*.cpp lib/*.c tools/*.cpp tools/*.c tools/*.h unittests/*.cpp)
-file( GLOB_RECURSE external lib/External/*.h lib/External/*.c lib/External/*.cpp)
+file( GLOB_RECURSE external lib/External/*.h lib/External/*.c lib/External/*.cpp isl_config.h)
 list( REMOVE_ITEM files ${external})
 
 set(check_format_depends)
 set(update_format_depends)
 set(i 0)
 foreach (file IN LISTS files)
   add_custom_command(OUTPUT polly-check-format${i}
     COMMAND clang-format -sort-includes -style=llvm ${file} | diff -u ${file} -