How can I compile PL/SQL source saved in table?

Try this:

declare
 text varchar2(4000);
begin
 select code into text from bkp_table;
 execute immediate 'create or replace ' || text;
end;
/

Ok this works if all lines of code are stored in single line. If you want to execute code that is stored in multiple lines you should go for something like:

declare 
  text varchar2(32767);
begin
  select listagg(text, ' ') within group (order by line) into text from all_source where name = 'MYPROC';
  execute immediate 'create or replace ' || text;
end;
/

Problem starts when 32767 characters is too few. In such case this may be a solution:

declare 
  text clob;
begin
for x in (select text from all_source where name = 'LONGTEST') loop
  text := text || x.text;
end loop;
  execute immediate 'create or replace ' || text;
end;
/

Please also have a look on that why it is a bit odd thing.

EDIT

As suggested changed to dbms_lob and in that case clob needs to be initialised:

declare 
  text clob := ' ';
begin
for x in (select text from all_source where name = 'LONGTEST') loop
  dbms_lob.append(text, x.text);
end loop;
  execute immediate 'create or replace ' || text;
end;
/