Give up the inlining expansion for strcmp/strncmp/memcmp on a target where the...

Give up the inlining expansion for strcmp/strncmp/memcmp on a target where the...

Give up the inlining expansion for strcmp/strncmp/memcmp on a target
where the type of the call has same or narrower presicion than unsigned
char.
Change char to unsigned char for strcmp/strncmp when expand them to
a sequence of byte comparisons.

Due to C standard section 7.24.4:

The sign of a nonzero value returned by the comparison functions memcmp,
strcmp, and strncmp is determined by the sign of the difference between
the values of the first pair of characters (both interpreted as unsigned
char) that differ in the objects being compared.

bootstraped and tested on both X86 and Aarch64. no regression.

From-SVN: r262907