cmake support

[Jason Bacon <outpaddling%yahoo.com@localhost>]

Low priority, but possibly simple issue:

Has anyone been looking at improving support for cmake, particularly out 
of source builds?

FreeBSD ports has

USES=    cmake:outsource

As far as I can tell, pkgsrc requires some manual fudging to accomplish 
this:

Example from wm/awesome and numerous others:

CONFIGURE_DIRS=    ${WRKDIR}/build
CMAKE_ARG_PATH=    ${WRKSRC}

pre-configure:
    ${RUN} mkdir -p ${WRKDIR}/build

There are 71 packages using CMAKE_ARG_PATH and from a quick visual scan, 
it looks like most of them use it along with

CONFIGURE_DIRS=    '.*build'

for out of source builds.

Is this worth adding support for in mk?