deref process label in the process itself via instance_name attribute

[hiyuh]

w/ proposed regression issueX,

entity issueX is
begin
end entity issueX;

architecture a of issueX is

begin

    p : process
    begin
        report p'instance_name;
        wait;
    end process p;

end architecture a;

then i got,

$ NVC_LIBPATH=./lib/std:./lib/ieee:./lib/nvc NVC_CYG_LIB=./src ./src/nvc.exe -a test/regress/issueX.vhd
** Error: undefined identifier P
        File test/regress/issueX.vhd, Line 11
      report p'instance_name;
             ^

[nickg]

Fixed by the above