regen/embed.pl: Certain flags are mutually exclusive

It makes no sense to specify more than one of A C X, nor more than one
of A C E.  This commit enforces that, showing one entry in embed.fnc
that needed to be changed.

Author: khwilliamson

embed.fnc

@@ -2069,7 +2069,7 @@ Cp	|const char *|moreswitches					\
 Adp	|void	|mortal_destructor_sv					\
 				|NN SV *coderef 			\
 				|NULLOK SV *args
-CRTXip	|char * |mortal_getenv	|NN const char *str
+CRTip	|char * |mortal_getenv	|NN const char *str
 Cdp	|void	|mortal_svfunc_x|SVFUNC_t f				\
 				|NULLOK SV *p
 Adop	|const struct mro_alg *|mro_get_from_name			\

regen/embed.pl

@@ -142,6 +142,14 @@ sub generate_proto_h {
             warn "It is nonsensical to require the return value of a void function ($plain_func) to be checked";
         }
 
+        my $count = 0;
+        $count++ while $flags =~ /[ACX]/g;
+        die_at_end "$plain_func: A, C, and X flags are mutually exclusive"
+                                                                if $count > 1;
+        $count = 0;
+        $count++ while $flags =~ /[ACE]/g;
+        die_at_end "$plain_func: A, C, and E flags are mutually exclusive"
+                                                                if $count > 1;
         die_at_end "$plain_func: S and p flags are mutually exclusive"
                                             if $flags =~ /S/ && $flags =~ /p/;
         if ($has_mflag) {