configure: when cross-compiling, set $TOOLPREF and use it.
(Patch by Adrien Nader!)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13854 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
configure: add a special case to test for BSD sockets for mingw.
(Patch by Adrien Nader!)

I tried to use "hasgot" to test it but proved too difficult since you
must #include <winsock2.h> to make link succeed (windows magic) which
then makes gcc complain about the prototype being wrong.

Since windows already needs a special case in order to add -lws2_32 and
since we know for sure it will be available, skip the hasgot test and
check $target directly.
configure: add a special case to test for BSD sockets for mingw.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13855 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
build: select win32 variants of unix and graph for mingw.
(Patch by Adrien Nader!)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13856 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
configure: store $target and $host in the build configuration.
(Patch by Adrien Nader!)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13857 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02