util/find-doc-nits: read full declarations as one line in name_synopsis()

util/find-doc-nits: read full declarations as one line in name_synopsis()

name_synopsis was reading physical SYNOPSIS lines.  This changes it to
consider a declaration at a time, so we treat a C declaration that's
been broken up in several lines as one.

This makes it mandatory to end all C declarations in the SYNOPSIS with
a semicolon.  Those can be detected in two ways:

1.  Parsing an individual .pod file outputs this error:

    doc/man3/SOMETHING.pod:1: Can't parse rest of synopsis:

     int SOMETHING_status(SOMETHING *s)
     int SOMETHING_start(SOMETHING *s)

    (declarations not ending with a semicolon (;)?)

2.  Errors like this:

    doc/man3/SOMETHING.pod:1: SOMETHING_status missing from SYNOPSIS
    doc/man3/SOMETHING.pod:1: SOMETHING_start missing from SYNOPSIS

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12452)