fix internal __ieee754_expf and __ieee754_logf calls

fix internal __ieee754_expf and __ieee754_logf calls

The recently added new math code inlines error handling instead of using
error handling wrappers around __ieee754* internal symbols, and thus the
__ieee754* symbols are no longer provided.

However __ieee754_expf and __ieee754_logf are used in the implementation
of a number of other math functions.  These symbols are safe to redirect
to the external expf and logf symbols, because those names are always
reserved when single precision math functions are reserved and the
additional error handling code is either not reached or there will be
an error in the final result that will override an internal spurious
errno setting.

For consistency all of __ieee754_expf, __ieee754_logf and __ieee754_powf
are redirected using a macro.