uClibc defines _SC_LEVEL1_ICACHE_LINESIZE and _SC_LEVEL1_DCACHE_LINESIZE
but the corresponding sysconf calls returns -1, which is a valid result,
meaning that the limit is indeterminate.

Handle this situation using the fallback values instead of crashing due
to an assertion failure.

Signed-off-by: Carlos Santos <casantos@redhat.com>
Message-Id: <20191017123713.30192-1-casantos@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>