Include version.c from build dir in preference to source dir

This should fix out-of-source-tree builds from a tarball, which
otherwise would use the autogenerated $(objdir)/version.c for building
the library, but the pre-packaged $(srcdir)/version.c for the
executable. This is because the latter was included directly from main.c
by #include "version.c". By changing to #include <main.c> instead, we get
to use the new auto-generated one instead if anything's been changed.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

main.c

@@ -72,7 +72,7 @@ static void init_stoken(struct openconnect_info *vpninfo,
 /* A sanity check that the openconnect executable is running against a
    library of the same version */
 #define openconnect_version_str openconnect_binary_version
-#include "version.c"
+#include <version.c>
 #undef openconnect_version_str
 
 int verbose = PRG_INFO;