libm: Fix log-related symbol aliases.

- Do the weak alias dance for log, log2, log10, log1p, and their
f/l variants.

(Not strictly necessary for log2 and log10 since nothing in the
math library itself uses them -- only a computer scientist would
use log2 and only an engineer would use log10 -- but let's just do
it the same for all our forestry.)

- Provide long double aliases on vax.

- Sprinkle RCS ids.

libm: Factor out common expected symbol list.

Should substantially reduce the maintenance burden.

libm: Factor out common expected symbol list.

Should substantially reduce the maintenance burden.