win64-underscore patch

configure.ac

@@ -314,6 +314,13 @@ if test x$TARGET = xX86 || test x$TARGET = xX86_WIN32 || test x$TARGET = xX86_64
     fi
 fi
 
+if test x$TARGET = xX86_WIN64; then
+    LT_SYS_SYMBOL_USCORE
+    if test "x$sys_symbol_underscore" = xyes; then
+        AC_DEFINE(SYMBOL_UNDERSCORE, 1, [Define if symbols are underscored.])
+    fi
+fi
+
 case "$target" in
      *-apple-darwin10* | *-*-freebsd* | *-*-openbsd* | *-pc-solaris*)
        AC_DEFINE(FFI_MMAP_EXEC_WRIT, 1,