What about a line processing approach? If function declarations always begin with a left brace at column 0 and end with a right brace at column 0, the following should work:

my ($prev, $type, $func, $args, $body);
while (<>) {
    if (/^\{/) {
        # maybe check for structs/classes here if necessary
        ($type, $func, $args) = split(' ', $prev, 3);
        $body = '';
    } elsif (/^\}/) {
        # ... process the function here ...
        $func = undef;
    } else {
        if (defined($func)) {
            $body .= $_;
        } else {
            $prev = $_;
        }
    }
}
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As noted in the code, you might have to check for structs and/or classes.