Fix local #include to use quoted form

Fix local #include to use quoted form

.h include files from the same folder or addressed relatively to the
same folder should be #included using quoted form in MSVC. The angled
form is reserved for include files from folders specified using /I
path.

Using angled form, MSVC fails to locate local #include file, unless
current folder is added to the include search path: /I .
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20171012103448.7632-1-simon@rozman.si>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15622.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>