Sam Yates authored 6 years ago and Benjamin Cumming committed 6 years ago

Fixes issue #517.

Deprecate the IBM xlC compiler.
xlC generates code that is an order of a magnitude slower than gcc, while generating spurious warnings, and requiring hacks and workarounds to pass all tests.
Supporting it makes no sense.

* Add test and fatal error for xlC detection in CheckCompilerXLC.cmake.
* Move xlC 13 misdetection work around to CheckCompilerXLC.cmake.
* Remove xlC-specific compatibility workarounds from code.