mdemo2-make.test on MinGW failure in libtool 2-0 and head.

[Peter Ekberg]

Hi!

I have looked at the reason why the mdemo2-make.test fails
on MinGW.

The reason is that the mlib_func symbol is not properly
exported from libmlib (i.e. not present in the import lib).

I see two solutions to make the test pass.

1. Add ' -export-symbols-regex "mlib_func"' to libmlib_la_LDFLAGS
in tests/mdemo/Makefile.am.

2. Add an dllexport declaration in tests/mdemo/mlib.c #ifdefed for
MinGW. Or reuse the one from libltdl:
LT_SCOPE int mlib_func(int, char **);

I don't know if the mlib_func symbol is supposed to be exported
from mlib without an explicit request to do so as in 1 above.

I have this guess as to why exporting symbols from mdemo/foo1
works without an explicit export anywhere but fails in mlib:

When mdemo/foo1 is linked, there is no mention of any exported
symbol, so every non-static symbol is exported. When mdemo/mlib
is linked, it is linked with the convenience library libltdlc
which as a lot of __declspec(dllexport)ed symbols. I think
these dllexports makes the linker assume that no other symbols
are to be exported.

Which of 1 and 2 seems like the best solution? I have verified
that both approaches solves the mdemo2 tests on branch-2-0.

Cheers,
Peter