nir: Make nir_create_function() strdup the function name.

nir: Make nir_create_function() strdup the function name.

glsl_to_nir passes in the ir_function's name field; we were copying the
pointer, but not duplicating the memory.

We want to be able to free the linked GLSL IR program after translating
to NIR, so we'll need to create a copy of the function name that the NIR
shader actually owns.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>