Since commit v2.6.0~388 (Added build rule variables
CMAKE_<LANG>_ARCHIVE_..., 2008-01-29) we use separate "ar cr ..." and
"ar r ..." steps to incrementally add a large list of object files to an
archive.  Since the "r" command replaces existing objects of the same
name in an archive, if multiple objects have the same file name and
appear in separate append steps then one overwrites the other.  Instead,
use "ar cq ..." and "ar q ..." to always append to the archive.

We already remove the archive before creating it so this will not cause
objects to be appended to existing archives on incremental rebuilds.