$_ = do{ local $/; <DATA> };
s[("[^\n"]*?")|("[^\n"]+?\n[^"]+?")][ ##"
    $1 || do{ (my $x = $2) =~ s[\s+][ ]g; $x }
]ge;
print;
"boom"
hello "" bill
hello "  " bill
"baz hello jock"
"boom2"
 abc "baz2 hello2 jock2 "