build: fix bleeding whitespace

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@203531 91177308-0d34-0410-b5e6-96231b3b80d8
build: use LLVM build routines

Check if the compiler actually supports the flags that are being added.
Previously, the compiler flags would be used improperly push the flags to the
compiler.  Particularly, on Darwin, the option would be pushed to the compiler
even if it does not support it.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@203532 91177308-0d34-0410-b5e6-96231b3b80d8