Merge bmake-20151201

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge bmake-20130904

Merge bmake-20130730
Main feature of interest is .MAKE.JOB.PREFIX=
to suppress --- job --- tokens.

Update to bmake-20130330

Missed adding Makefile.config and unit-tests/Makefile should
allow FreeBSD make to do 'obj'.

Approved by: marcel (mentor)

Merge bmake-20130123

Approved by: marcel (mentor)

Merge bmake-20121111
Also pay attention to MK_SHARED_TOOLCHAIN.

Approved by: marcel (mentor)

Add bmake to the build and allow it to be installed as make(1) instead
of FreeBSD's make by setting WITH_BMAKE. The WITH_BMAKE build makes it
easy for people to switch while working out the kinks -- think ports
tree here. The option will be removed in due time.

Submitted by: Simon Gerraty (sjg@juniper.net)