This was previously fixed by commit d46590910c (Check*CompilerFlag: Do
not set result as a normal variable too, 2020-09-21, v3.18.3~1^2^2), but
was regressed by refactoring in commit 90dead024c (CheckCompilerFlag:
unified way to check compiler flags per language, 2020-09-25,
v3.19.0-rc1~88^2) due to the changes being developed concurrently.
Fix it again, and add a test case.
Fixes: #21207
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 conversion of Check<Lang>CompilerFlag, SourceCompiles, and
SourceRuns over to the new functions has the possibility of breaking
projects that had functions with those existing names.
To reduce the possibility of collisions we now have all the
legacy code call functions that start with `cmake_`, and users
will need to explicitly include the new modules to get the
non-prefixed versions
Fixes: #21359
