glsl: inline functions with unsupported return type before converting to nir

glsl: inline functions with unsupported return type before converting to nir

glsl_to_nir doesn't expect non-vector/scalar return types in functions.

Fixes: 7e60d5a501f311fa5e7bca5335adc6013dc1aeb9
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3058
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3060
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Tested-by: Witold Baryluk <witold.baryluk@gmail.com>
Reviewed-by: Witold Baryluk <witold.baryluk@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5333>