message: Replace FORCE rule in src/Makefile.am
  .. for the xversionkeys.h file. Tested to build under mingw64/msys2 on
  Windows 10.
diff: @@ -224,7 +224,7 @@ obj/build.h: FORCE
  $(abs_top_srcdir)
  libbitcoin_util_a-clientversion.$(OBJEXT): obj/build.h
  -xversionkeys.h: FORCE
  +xversionkeys.h: $(top_srcdir)/contrib/devtools/xversionkeys.py $(top_srcdir)/src/xversionkeys.dat
  $(PYTHON) $(top_srcdir)/contrib/devtools/xversionkeys.py > $(abs_top_builddir)/src/xversionkeys.h < $(srcdir)/xversionkeys.dat
  BUILT_SOURCES= xversionkeys.h
  