[PATCH] Define NAN as (0.0f / 0.0f)

Runtimes OpenCL
#1

We can't use __builtin_nanf(""), because string literals are in the
constant address space, and __builtin_nanf only accepts pointers
to values in the default address space.

#2

We can't use __builtin_nanf(""), because string literals are in the
constant address space, and __builtin_nanf only accepts pointers
to values in the default address space.

This really should be fixed in clang and not worked around in the library