use strict;
use warnings;

my $s = <<"GROK";
"boom"
hello "" bill
hello "  " bill
"baz
  \t   hello
            jock"
"boom2"
 abc "baz2
hello2     \t 
            jock2  "
GROK

$s =~ s{"([^"]*)"}
       { if ($1 =~ tr/\n//) {
            my $x = $1;
            $x =~ s/[ \t]*\n[ \t]*/ /g;
            '"' . $x . '"';
         }
         else {
            '"' . $1 . '"';
         }
       }eg;