embed.pl - sort and dedupe flags in embef.fnc as part of tidy

This ensures we use a canonical string for each possible flag variant,
which makes it easier to search for flags with a given flag signature.

It also exposed a mutex bug in flag handling which caused
PerlEnv_putenv to be improperly marked as static, when it is in fact
static inline.

To validate there aren't any issues like this remaining in the script
I set it up so the flags were shuffled during processing and ran
embed.pl in a loop for a while and none of the output files changed,
so I assume there are no further such issues.

This patch also includes some basic validation of the flags so that if
someone misses a line continuation the following lines are not treated
as a new definition without any flags. I also ran perltidy on it
according to the rules contained within the file.

Author: demerphq