stress-ng: add config menu to select external libraries

stress-ng: add config menu to select external libraries

Backport upstream e0c4d324a, which lets a LIB_* variable be emptied to skip
that library's check. Drop 001-disable-extra-stressors.patch, which hardcoded
the same choice, and drive it from a Config.in menu instead. Defaults keep the
previously built set of stressors: only crypt, aio, bsd, jpeg, kmod, sctp and
zlib are probed. apparmor, EGL, GBM, GLES2, IPSec_MB and Judy have no OpenWrt
package, so they are never probed. Drop the backport once it is in a release.

Signed-off-by: Alexandru Ardelean <redacted>