Mock openvpn_exece on win32 also for test_tls_crypt

Mock openvpn_exece on win32 also for test_tls_crypt

This function is needed to commpile on win32 as run_command.c defines it
on Unix Linux but on windows it is defined in win32.c which pulls in too
many other unresolvable symbols.

Patch v2: Also add mock_win32_execve.c to automake files

Change-Id: I8c8fe298eb30e211279f3fc010584b9d3bc14b4a
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20230712095412.570106-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26849.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>