subsurface-configure.pri: pkg-config detection change

This is a small change, but it seems to work as expected on both
Linux and Win32. What happens if 2> NUL > NUL is used on Win32
for cmd.exe is that the output of both stdout and stderr seems
to pipe into NUL and pkg-config is always reported as missing.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
subsurface-configure.pri: enable the libusb detection stage

The commented out step should work as expected (in theory).

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
subsurface-configure.pri: add another libxml/libxslt detection stage

libxml and libxslt use custom -config scripts which brake
qmake and make on Win32. The output of executing a .sh or .cmd
script with the same name produces garbled output. The output
of executables with the same name is untested, but a bit excessive
as a solution.

To work around the issue add another detection stage, which checks
if the previous output from (e.g.) xml2-config is empty and try
to use pkg-config instead.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
subsurface-configure.pri: add a libiconv dependency

This is a bit crude of a solution, but the Win32 version
of libxml (or at least some versions) seem to require libiconv,
thus we add the library with pkg-config if it is available.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Try hard not to link against a shared libdivecomputer

Versioning is wrong. It's not a library shared with other projects. And at
least on Mac and Windows we bundle it with the app, anyway.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
We already try to link against libusb anyway

No need for the special case here.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>