qga: fix w32 breakage due to missing osdep.h includes

qga: fix w32 breakage due to missing osdep.h includes

requester.h relied on qemu/compiler.h definitions to
handle GCC_FMT_ATTR() stub, but this include was removed as part
of scripted clean-ups via 30456d5:

  all: Clean up includes

under the assumption that all C files would have included it via
qemu/osdep.h at that point. requester.cpp was likely missed
due to C++ files requiring manual/special handling as well as
VSS build options needing to be enabled to trigger build failures.

Fix this by including qemu/osdep.h. That in turn pulls in a
macro from qapi/error.h that conflicts with a struct field name
in requester.h, so fix that as well by renaming the field.

While we're at it, fix up provider.cpp/install.cpp to include
osdep.h as well.

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>