bootstrap / CMake infra should have an option for disabling libnuma dependence

[anyzelman]

In some cases (e.g., building for Windows), the POSIX Threads requirement can be mitigated, but no known full and native mitigation for the libnuma dependence is known to me. The code base does support _GRB_NO_LIBNUMA, but currently the CMake infra does not have this variable, causing it to still look for the libnuma dependence (and, on e.g. Windows, fail even if the code might build with -D_GRB_NOLIBNUMA).

This issue is for the following three proposed fixes:

• rename GRB_NOLIBNUMA to ALP_NO_LIBNUMA;
• have the addition of this flag propagate through CMake and bootstrap (i.e., introduce a bootstrap option a la --disable-libnuma);
• on being given this flag, have the CMake infra not look for the libnuma dependence.

[anyzelman]

Tag @alberto-scolari and suggesting inclusion for the next release (0.9)