Build fails with GNU make 4.4: No rule to make target 'FORCE'

[whitslack]

Issue and Steps to Reproduce

Using GNU Make 4.4, the build of v0.12.1 (and master at 0d756ff) fails with:

make: *** No rule to make target 'FORCE', needed by 'wallet/db_sqlite3_sqlgen.c'.  Stop.

This may be due to a regression in Make, but it's easy to work around: simply define FORCE as a normal rule, not a double-colon rule. It's unclear why it was defined as a double-colon rule in the first place since it's only defined once.

Please change:

FORCE::

to:

FORCE:

With that change, all is well with GNU Make 4.4.