embed.pl - the 's', 'S', 'i' and 'I' flags are mutually exclusive

embed.pl - the 's', 'S', 'i' and 'I' flags are mutually exclusive

We had a bug where we processed the first one in the flags definition. Sorting
the flags or rearranging them changes the output, which shouldn't happen.

This also fixes the handling and specification of PerlEnv_putenv(), which was
marked "si" when it should have been marked "i". This required changing its
implementation from a Perl_ prefix to a S_ prefix and regenerating.

I have run embed.pl in a loop with a local patch to shuffle the flags to see
if there were any other order dependencies. No output files changed so I
assume with this patch we are free of such bugs.