add /force flag to build.bat (#757) #86

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	30m 13s
ci (a6osx, macos-12)	21m 51s
ci (ta6osx, macos-12)	31m 6s
ci (i3le, ubuntu-22.04)	13m 5s
ci (ti3le, ubuntu-22.04)	15m 57s
ci (a6le, ubuntu-22.04)	9m 23s
ci (ta6le, ubuntu-22.04)	12m 25s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 40s
ci (i3nt, windows-2022, vs)	11m 53s
ci (ti3nt, windows-2022, vs)	15m 15s
ci (a6nt, windows-2022, vs)	12m 28s
ci (ta6nt, windows-2022, vs)	15m 56s
ci (ta6nt, windows-2022, gcc)	13m 7s
	3h 31m 19s

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