[Rd] building windows packages under wine/linux and cross-compiling.

[Hin-Tak Leung]

Had some fun today, and thought it might be a good idea to share
and possibly for inclusion to R/src/gnuwin32/README.packages .

Wine/linux : while R, ActiveState Perl, mingw all works alright under 
wine, the blocking issue is Rtool's cygwin dependency. forking
(as much of make and sh is forking sub-processes)
on posix-on-win32-on-posix currently doesn't work.
(http://wiki.winehq.org/CygwinSupport)

Cross-compiling: The instruction in R/src/gnuwin32/README.packages 
essentially works, with one missing detail: "R_EXE=/usr/bin/R" is also 
needed. Thus it should be:

     make R_EXE=/usr/bin/R PKGDIR=/mysources RLIB=/R/win/library \
             pkg-mypkg
     make P_EXE=/usr/bin/R KGDIR=/mysources RLIB=/R/win/library \
             pkgcheck-mypkg

Hin-Tak Leung