mod/file2alias: make modpost compile on darwin again

mod/file2alias: make modpost compile on darwin again

commit 017b5918bf81dc2b432543fabad9d0365ce238ca breaks cross compiling
the linux kernel on darwin hosts.
This fix introduce some minimal glue to adopt linker section handling
for darwin hosts.

Signed-off-by: Andreas Bießmann <andreas@biessmann.de>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Jochen Friedrich <jochen@scram.de>
CC: Samuel Ortiz <sameo@linux.intel.com>
CC: "K. Y. Srinivasan" <kys@microsoft.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Tested-by: Bernhard Walle <bernhard@bwalle.de>