Build on OS X.
Build on OS X.

- Change libcoreclr probing to use find_library instead of find_path.
- Enable @rpath on OS X and set CMake policy 0042 to NEW.

manu-silicon/llilc,dkorolev/llilc,marksantos/llilc,tempbottle/llilc,marksantos/llilc,JosephTremoulet/llilc,libengu/llilc,pgavlin/llilc,richardlford/llilc,russellhadley/llilc,mmitche/llilc,JosephTremoulet/llilc,manu-silicon/llilc,dotnet/llilc,russellhadley/llilc-original,dotnet/llilc,russellhadley/llilc-original,adiaaida/llilc,russellhadley/llilc,libengu/llilc,dkorolev/llilc,richardlford/llilc,adiaaida/llilc,mmitche/llilc,JosephTremoulet/llilc,tempbottle/llilc,swaroop-sridhar/llilc,AndyAyersMS/llilc,kyulee1/llilcjit,tempbottle/llilc,BruceForstall/llilc,dkorolev/llilc,russellhadley/llilc,swaroop-sridhar/llilc,adiaaida/llilc,erozenfeld/llilc,pgavlin/llilc,marksantos/llilc,mmitche/llilc,erozenfeld/llilc,mmitche/llilc,BruceForstall/llilc,richardlford/llilc,erozenfeld/llilc,AndyAyersMS/llilc,kyulee1/llilcjit,dotnet/llilc,libengu/llilc,libengu/llilc,manu-silicon/llilc,pgavlin/llilc,russellhadley/llilc-original,BruceForstall/llilc,swaroop-sridhar/llilc,erozenfeld/llilc,kyulee1/llilcjit,russellhadley/llilc-original,AndyAyersMS/llilc