message: Fix unportable test(1) operator in configure
  '=' is the standard one, only some shells support '=='.
diff: @@ -274,7 +274,7 @@ AS_IF([test "x$have_cld2" = "xyes"],
  -if test "x$GXX" == "xyes"; then
  +if test "x$GXX" = "xyes"; then
  AX_CXX_CHECK_FLAG([-Wall],[],[], [CXXFLAGS="$CXXFLAGS -Wall"])
  AX_CXX_CHECK_FLAG([-Wextra],[],[], [CXXFLAGS="$CXXFLAGS -Wextra"])
  fi
  