The variables recently added by commit b9d36826 (Add 'CMAKE_GCC_AR' and
'CMAKE_GCC_RANLIB' variables, 2017-03-08) are more appropriately managed
with language-specific names rather than toolchain-specific names.
The `cmake_policy(SET)` call triggers `CMP0011` warnings when this
module is used in a project that does not set `CMP0011` to NEW. We
could avoid these with a `cmake_policy` PUSH/POP pair, but it is simpler
to adjust our code to not trigger `CMP0054` in the first place.
Brad King