make version on Windows, cygpath problems, ..

Hi all,

I was once curious why 386161779b55755f145106cd53c5df80967e1c3b
was necessary, so I tried to install more versions of make and indeed make 3.81
does not like mixed paths (cygpath -m) and needs unix paths in make's rules.
Because of this there are many problems, we need
gb_Helper_convert_native and similar things.

We already check for our patched make and print warning [1],
so I am wondering, could we force people to use it ?

It's broken for make 3.81 since a75873dea15719b5216cfd0476d30003ffc76e80 anyway
and nobody is complaining so far (but it's +- only a week).

I am optimistic and I think by forcing people to use make 3.82 on cygwin,
we could remove solenv/gbuild/BuildDirs.mk and use ~only mixed paths.
There still will be problems (realpath is producing unix path,
some programs need unix paths [2], ..)
but hopefully it will be better.

Do you think it's worth a try ?

Matus

[1] http://cgit.freedesktop.org/libreoffice/core/tree/configure.in#n11067
[2] http://cgit.freedesktop.org/libreoffice/core/tree/clucene/source/Makefile#n32