[RFC] external compiler support

[Simon J. Gerraty]

On Wed, 27 Feb 2013 17:59:52 -0600, Brooks Davis writes:
>I'm not arguing against the proposed indirection at all.  The long term
>benefits are quite clear, it just doesn't do me much good in the current
>world order.

Ah - understood.

>> CFLAGS_LAST.clang +=3D -isystem ${STAGE_OBJTOP}/usr/include/clang/3.2
>> CXXFLAGS_LAST +=3D ${CFLAGS_LAST.${COMPILER_TYPE}}
>
>Hmm, I've not had to do that, but it seems likely that similar things
>could be required.

I was even more suprised to find that clang needed 

-isystem ${STAGE_OBJTOP}/usr/include/c++/${GCCVER:U4.2}

.meta files are great for finding out what the compiler is really doing ;-)

Of course all these -isystem's are needed because I use -nostdinc to
avoid accidentally pulling headers from /usr/include.
With sysroot support that wouldn't be necessary.

>I think remember the issue now.  The problem was that I was setting a
>variable (SYSROOT) that would cause additions to CFLAGS.  Because the
>crunch environment is set by crunchgen I wasn't able to figure out a good

looks like crunchgen uses 'env MAKEOBJDIRPREFIX=$(MAKEOBJDIRPREFIX) $(MAKE)'
not env -i, so if you export SYSROOT it should be seen.

>An example of a problem boot related Makefile is
>sys/boot/i386/gptboot/Makefile.

Yep, and this is where CFLAGS_LAST comes in handy with 

CFLAGS+= ${CFLAGS_LAST}

in bsd.init.mk or bsd.sys.mk