add new F_OFD_* macros to fcntl.h (open file description locks)

open file description locks are inherited across fork and only auto
dropped after the last fd of the file description is closed, they can be
used to synchronize between threads that open separate file descriptions
for the same file.

new in linux 3.15 commit 0d3f7a2dd2f5cf9642982515e020c1aee2cf7af6
prune math code on archs with binary64 long double

__polevll, __p1evll and exp10l were provided on archs when long double
is the same as double. The first two were completely unused and exp10l
can be a wrapper around exp10.
fix exp10l.c to include float.h

the previous commit was a no op in exp10l because LDBL_* macros
were implicitly 0 (the preprocessor does not warn about undefined
symbols).