elfutils: Add host build

elfutils: Add host build

Needed for glib2 host build:

gresource-tool.c:32:20: fatal error: libelf.h: No such file or directory
 #include <libelf.h>

Changed PKG_LICENSE to the SPDX version.

Switched build dependency for argp-standalone to !USE_GLIBC. argp is a
glibc extension. Treat it as such.

Adjusted patch to use strerror_l, which works properly with both glibc
and musl. The patch errors under glibc with:

dwfl_error.c:158:7: error: ignoring return value of 'strerror_r', declared
with attribute warn_unused_result [-Werror=unused-result]
       strerror_r (error & 0xffff, s, sizeof(s));

void casting does not fix the error.

Signed-off-by: Rosen Penev <rosenp@gmail.com>