qtgraphs defines a target in one directory, and then calls
qt_internal_extend_target with NO_UNITY_BUILD_SOURCES in another
subdirectory scope. That in turn calls set_source_files_properties
but only for the latter subdirectory, and not the main target
directory.
Because CMake has per-directory-scope source file properties, the
'no unity sources' option was effectively ignored.
When using CMake 3.18, make sure to specify the TARGET_DIRECTORY
option so that the source file properties are added to the scope of
the defining target.
Pick-to: 6.5 6.6 6.7
Change-Id: I4190d4073a2955aa7053b5faaaa57f683bc768a2
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
081e50d768