clang (since r280553) allows pointer casts in function overloads,
so we need to disambiguate the second argument.
clang might be smarter about overloads in the future
(see ⚙ D24113 Allow implicit conversions between incompatible pointer types in overload resolution in C.), but let's be safe in libclc anyway.
Signed-off-by: Jan Vesely <email@example.com>