Invoke AppleClang via system compiler shims

Fixes #171

Author: nickelpro

cmake/appleclang-toolchain.cmake

@@ -16,8 +16,10 @@
 
 include_guard(GLOBAL)
 
-set(CMAKE_C_COMPILER clang)
-set(CMAKE_CXX_COMPILER clang++)
+# Prevent PATH collision with an LLVM clang installation by using the system
+# compiler shims
+set(CMAKE_C_COMPILER cc)
+set(CMAKE_CXX_COMPILER c++)
 
 if(BEMAN_BUILDSYS_SANITIZER STREQUAL "MaxSan")
     set(SANITIZER_FLAGS