Fix the language checks added by commit 90dead024c (CheckCompilerFlag:
unified way to check compiler flags per language, 2020-09-25,
v3.19.0-rc1~88^2), commit 10ae907de0 (CheckSoureCompiles: Add a unified
way to check if a source compiles, 2020-09-14, v3.19.0-rc1~118^2~1), and
commit 357e2ef429 (CheckSoureRuns: Add a unified way to check if a
source runs, 2020-09-14, v3.19.0-rc1~118^2) to work when variables of
the language names are set.
Fixes: #21500
The warning emmitted by GCC for invalid options have been updated to
read "command-line option XXX is valid ..." instead of "command line
option XXX is valid ...". Update the regex to make it valid with both
the old and new warning message.
Fixes: #21275