Fix CMAKE_(C|CXX|Fortran)_STANDARD_LIBRARIES helpstrings (#14622)

s/defalut/default/

Reported-by: Stephan Tolksdorf <st@quanttec.com>
Merge topic 'lang-flag-var-helpstrings' into next

5d2452d Fix CMAKE_(C|CXX|Fortran)_STANDARD_LIBRARIES helpstrings (#14622)