Check for va_copy declaration

ctx.c contains a workaround for systems without va_copy() support.
Improve this workaround in the way which is described in the autoconf
manual.

Also check for va_copy declaration in configure time.

Fixes #160.

Author: pasis

configure.ac

@@ -33,6 +33,7 @@ AC_ARG_ENABLE([cares],
 
 AC_SEARCH_LIBS([socket], [network socket])
 AC_CHECK_FUNCS([snprintf vsnprintf])
+AC_CHECK_DECLS([va_copy], [], [], [#include <stdarg.h>])
 
 if test "x$enable_tls" != xno; then
     PKG_CHECK_MODULES([openssl], [openssl],

src/ctx.c

@@ -50,9 +50,10 @@
 #include "resolver.h"
 #include "util.h"
 
-/* Workaround for visual studio without va_copy support. */
-#if defined(_MSC_VER) && _MSC_VER < 1800 || defined(__HAIKU__)
-#define va_copy(d, s) ((d) = (s))
+/* Workaround for systems without va_copy support. */
+#if defined(_MSC_VER) && _MSC_VER < 1800 || \
+    !defined(_MSC_VER) && !defined(HAVE_DECL_VA_COPY)
+#define va_copy(d, s) (memcpy(&d, &s, sizeof(va_list)))
 #endif
 
 /** Initialize the Strophe library.