package/safeclib: fix armv7 and sparc builds

Fix the following build failure on armv7 and sparc raised since bump to
version 3.7.1 in commit cc27267a and
https://github.com/rurban/safeclib/commit/b90c52b1691fe82ce0a0681a503e1d45584f0162:

In file included from perf_memcpy32_s.c:7:
perf_private.h: In function 'rdtsc':
perf_private.h:72:3: error: 'asm' undeclared (first use in this function)
   72 |   asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
      |   ^~~

Fixes:
 - http://autobuild.buildroot.org/results/ceb13c071b1461eb6d73f5940d6b010095127f41



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