mod/file2alias: make modpost compile on darwin again

mod/file2alias: make modpost compile on darwin again

commit 27225d60e5ace0d5ad42124daca97a232ca0186a 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>