Add finite symbol for vector log2

[fpetrogalli]

glibc remaps log2[f] to __log2[f]_finite. We need to make sure that the vector form of this symbol is available in libsleefgnuabi.so. One it is done, the correspondent gnuabi compatibility test must be activated. See https://github.com/shibatch/sleef/commit/450a746da01bfdea1bd9b404b4adf425aa12eb4d#diff-e5e7a421d82269193c02ad7fb6261d97R265 and https://github.com/shibatch/sleef/commit/450a746da01bfdea1bd9b404b4adf425aa12eb4d#diff-e5e7a421d82269193c02ad7fb6261d97R335