[compiler-rt] compiler-rt's CMake append_if function clashes with LLVM's, let's rename it to append_list_if

Doing s/append_if/append_list_if/, no functional change.

http://reviews.llvm.org/D5739



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@219860 91177308-0d34-0410-b5e6-96231b3b80d8