libm: Fix some whitespace issues in recent sincos additions.

s_sincos.c: use correct order of __weak_alias() arguments...

s_sincos.c: use __weak_alias and not __weak_reference.

Fixes build on NetBSD/macppc, thanks to hint from riastradh@

only alias sincos to sincosl when we don't have long doubles

Add sincos{,f,l} from FreeBSD