configure_file: Add support for indented cmakedefine
Optional spaces and/or tabs are now understood between the #
character
and the cmakedefine
/'cmakedefine01
words. This indentation is
preserved in the output lines.
Documentation and release notes have been updated. Tests have been added although this is minimal and only test for C++ validity of the output not that the define is actually indented, but I have no idea how to do that.
Fixes: #13037 (closed)