Chuck Atkins authored Feb 05, 2019 and Brad King committed Feb 25, 2019

In commit 6555286c (XL: Add C and C++ language level flags,
2017-04-27, v3.9.0-rc1~184^2) we added support for both the traditional
XL compiler and the Clang-based variant used on Linux.  The latter is
now handled by `Modules/Compiler/XLClang-{C,CXX}.cmake` using the
`XLClang` compiler id.  Drop the corresponding content from the
traditional XL compiler modules.