This makes a difference when projects compare things like
CMAKE_SOURCE_DIR with CMAKE_CURRENT_SOURCE_DIR and the source
directory has a trailing slash in the GUI. The command line cmake invocation
cleans the paths at the beginning, so such comparisons return true. But the
GUI currently passes the paths unmodified, so such comparisons return false.
Change the logic to sanitize the paths used through the GUI in the same way
that the command line invocation does.
Fixes: #21421
afa1d0d0e3
