[7] make sure -R has argument (directory) in m4 macro that tests avai…

…lability.

(should also be trivial enough, so I'm pushing it directly at my discretion)
without this it's possible that it only results in warning on a system
that doesn't actually support this flag (such as MacOS X) and subsequently
causes build failure.

examples/m4/ax_bundy_rpath.m4

@@ -41,8 +41,8 @@ if test x$rpath != xno; then
             BUNDY_RPATH_FLAG=-Wl,-R
         ],[ AC_MSG_RESULT(no)
             AC_MSG_CHECKING([whether -R flag is available in linker])
-            CXXFLAGS="$CXXFLAGS_SAVED -R"
-            CCFLAGS="$CCFLAGS_SAVED -R"
+            CXXFLAGS="$CXXFLAGS_SAVED -R/usr/lib"
+            CCFLAGS="$CCFLAGS_SAVED -R/usr/lib"
         AC_TRY_LINK([], [],
             [ AC_MSG_RESULT([yes; note that -R is more sensitive about the position in option arguments])
                 BUNDY_RPATH_FLAG=-R