package/makedumpfile: fix build on sparc64

package/makedumpfile: fix build on sparc64

Fix the following build failure on sparc64:

/home/giuliobenetti/autobuild/run/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/sparc64-buildroot-linux-gnu/9.3.0/../../../../sparc64-buildroot-linux-gnu/bin/ld: /tmp/ccylTux8.o: in function `find_kaslr_offsets':
/home/giuliobenetti/autobuild/run/instance-0/output-1/build/makedumpfile-1.6.8/makedumpfile.c:4017: undefined reference to `get_kaslr_offset'

Even if this build failure is only raised with version 1.6.8,
get_kaslr_offset was also undeclared on sparc64 in version 1.6.7

Fixes:
 - http://autobuild.buildroot.org/results/1421f54f7599bba62c0a4bd5c65ce21c8cc7ee1a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>