[PATCH] [libcxxabi] Remove strict dependency on llvm-config.

[Dan Albert]

>>! In D5016#5, @loladiro wrote:
> One issue is that, if there is a llvm-config executable in the path, it tried to use that, which I want to prevent (this happened to me while trying to rebuild with different options - libcxxabi wasn't installed anymore, but llvm-config depending on it still was). 

Well, if there's an invalid llvm-config on your system, you should probably remove llvm-config :) I think I can probably just reorder the if/elseif and get the behavior you want though, but that might cause issues with rerunning cmake on an already configured directory.

>>! In D5016#4, @loladiro wrote:
> Seems to work fine for me, modulo having to set -std=c++11 manually in the CXXFLAGS, which is automatically set in libcxx and could be here too. 

Interesting. Outside the realm of this patch, but I'll fix that too.

http://reviews.llvm.org/D5016