PATCH: [perl #41202] text->float gives wrong answer

PATCH: [perl #41202] text->float gives wrong answer

This changes to use Perl_strtod() when available, and that turns out to
be the key to fixing this bug.

S_mulexp10() is removed from embed.fnc to avoid repeating the
complicated prerequisites for defining Perl_strtod().  This works
because this static function already was defined before use in
numeric.c, and always called in full form without using a macro.

James Keenan fixed a file permissions problem originally introduced by
this commit, but the fix has been squashed into it.