vppinfra: c11 safe string functions

Add memcmp_s, strcmp_s, strncmp_s, strcpy_s, strncpy_s, strcat_s, strncat_s,
strtok_s, strnlen_s, and strstr_s C11 safe string API. For migrating extant
unsafe API, add also the corresponding macro version of each safe API,
clib_memcmp, clib_strcmp, etc.

In general, the benefits of the safe string APIs are to provide null pointer
checks, add additional argument to specify the string length of the passed
string rather than relying on the null terminated character, and src/dest
overlap checking for the the string copy operations.

The macro version of the API takes the same number of arguments as the unsafe
API to provide easy migration. However, it does not usually provide the full
aformentioned benefits. In some cases, it is necessary to move to the safe
API rather than using the macro in order to avoid some unpredictable problems
such as accessing memory beyond what it is intended due to the lack of the
passed string length.

dbarach: add a "make test" vector, and a doxygen file header cookie.

Change-Id: I5cd79b8928dcf76a79bf3f0b8cbc1a8f24942f4c
Signed-off-by: Steven <sluong@cisco.com>
Signed-off-by: Dave Barach <dave@barachs.net>