DynamoRIOConfig.cmake.in shouldn't check CMAKE_COMPILER_IS_GNUCC

_From [rnk@google.com](https://code.google.com/u/rnk@google.com/) on February 20, 2013 10:28:04_

Related to issue #384 , which is building with clang and is essentially complete.

This check gets included in the exported DynamoRIOConfig64.cmake. External projects that do find_project(DynamoRIO) shouldn't have to set CMAKE_COMPILER_IS_GNUCC. We do need some check that we're using the bfd linker instead of gold for now, although I think we can remove the linker script by using -Wl,-Ttext-segment=0x71000000 and --defsym=...

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1083_