Allocate empty function name in the string pool.

Allocate empty function name in the string pool.

Inside the grammar for function_identifier if the .function is null an
empty function name is allocated. This is allocated on the stack and
passed into TFunction as a pointer. TFunction just stores that pointer.

Later, when we access the name we will receive an invalid usage of a
stack allocated variable. This CL switches to using NewPoolTStringn for
the empty function name.