package/audit: force arm mode instead of Thumb mode

Fix the following build failure:

/tmp/ccY5gl3z.s:2145: Error: selected processor does not support `mcr p15,0,r2,c7,c10,5' in Thumb mode

Fixes:
 - http://autobuild.buildroot.org/results/9d18a0d360b2e2f9e87c55daedda62d6ce198bb9



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>