Alan W. Irwin authored Oct 21, 2019 and Brad King committed Oct 21, 2019

Fix the `COMPILE_LANGUAGE/CXX_COMPILER_ID` variant of the example to
have the same meaning as the `COMPILE_LANG_AND_ID` variant.  The
inconsistency was introduced by commit 808b8180 (Genex: CompileLang
and CompileLangAndId now match against a list of ids, 2019-05-30,
v3.15.0-rc1~11^2~1).

Fixes: #19862