The parsefloat routines -- which let us pass NaNs and infinities on to
strto(f|d|ld) -- come from NetBSD.
Also fix LP64's strtold to return a NaN, and fix all the architectures
to return quiet NaNs.
Also fix wcstof/wcstod/wcstold to use parsefloat so they support hex
floats.
Lots of new tests.
Bug: http://b/31101647
Change-Id: Id7d46ac2d8acb8770b5e8c445e87cfabfde6f111