Load fake.rb at `BTESTRUBY`

	So that `mkmf` checks work from `make run`, and also remove
	duplicate `$(MINIRUBYOPT)` which is used in `$(MINIRUBY)`.
	---
	 common.mk            | 8 ++++----
	 template/Makefile.in | 3 +--
	 template/fake.rb.in  | 2 ++
	 win32/Makefile.sub   | 2 +-
	 4 files changed, 8 insertions(+), 7 deletions(-)