create compile_commands.json in builddir

assuming that nothing breaks for existing users of the
compile_commands.json file, since they assume BUILDDIR=SRCDIR, so
nothing will change in those cases.

For building in a different directory than the source, the
compile_commands.json file is the only thing that regularly clobbers my
otherwise pristine SRCROOT

Change-Id: I344afa0bc7bb3eaa1eb888cd3558d3602090af5f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/143571
Tested-by: Jenkins
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

0 files changed, 0 insertions, 0 deletions