make macro into the environment of programs executed by make. This
has approximately the same function as gmake's export directive.
The form of a pseudo target was deliberately choosen to minimize work
for POSIX compatibility (Makefiles are not allowed to use any targets
starting with a dot and consisting only of uppercase letters except those
specified in the standard when they want POSIX compatible behaviour, so
such a Makefile can never contain .EXPORTVAR.)
Change the handling of macros coming from the environment: instead
of asking the environment for each variable we could not find otherwise
put all the environment variables in a special variable environment just
at start up.
This has been tested on the ports cluster by kris.
Submitted by: Max Okumoto <okumoto@ucsd.edu>
9e2faf2a2d