[libclc] Move functions definition from header clc_sincos_piby4.inc into clc_sincos_helpers.cl (#164028)
inline functions defined in clc_sincos_piby4.inc miss static specifier
and are deleted by EliminateAvailableExternallyPass when not inlined.
This PR fix the problem by removing inline and moving function
definition
into clc/lib/generic/math/clc_sincos_helpers.cl. It makes sense to put
all sin/cos helpers definitions in one file clc_sincos_helpers.cl.