Fix CMAKE_DISABLE_SOURCE_CHANGES for top of build tree
The change in !1380 (merged) added code of the form
file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR})
. This exposed an existing
bug in CMAKE_DISABLE_SOURCE_CHANGES
in which it does not recognize
that the top of the build tree itself is in the build tree. Fix that
now.
Fixes: #17933 (closed)
Topic-rename: fix-CMAKE_DISABLE_SOURCE_CHANGES-top-dir
Edited by Brad King