Fix builds with llvm/runtimes/compiler-rt after r354365

Compiler-rt doesn't include config-ix which was providing CheckSymbolExists to
the LLVM build. Add it to HandleLLVMOptions to fix this


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354389 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed