Add a test-case showing a failure when -std=c++11 is not added to the…

… C++ compiler arguments

Signed-off-by: Kate <kit-ty-kate@outlook.com>

test/blackbox-tests/test-cases/cxx-flags.t/cpp11.cpp

@@ -0,0 +1,8 @@
+#include <caml/misc.h>
+#include <caml/mlvalues.h>
+#include <iostream>
+
+extern "C" CAMLprim value cpp11(value _unit) {
+  std::cout << "Hi from C++11" << std::endl;
+  return Val_unit;
+}

test/blackbox-tests/test-cases/cxx-flags.t/cpp11.ml

@@ -0,0 +1,3 @@
+external cpp11 : unit -> unit = "cpp11"
+
+let () = cpp11 ()

test/blackbox-tests/test-cases/cxx-flags.t/dune

@@ -31,3 +31,12 @@
    (= %{architecture} arm64)))
  (action
   (write-file extra_flags.sexp "(-ccopt -Wl,-no_warn_duplicate_libraries)")))
+
+; will fail if :standard doesn't have -std=c++11 on OCaml >= 5.0
+(executable
+ (name cpp11)
+ (modules cpp11)
+ (foreign_stubs
+  (language cxx)
+  (names cpp11)
+  (flags -std=c++98 :standard)))

test/blackbox-tests/test-cases/cxx-flags.t/run.t

@@ -143,3 +143,11 @@ one can extend link flags in env
   $ dune rules sub/main.exe --profile some-profile  | tr -s '\n' ' ' |
   > grep -ce "Main.cmx$GCC_LF_LIB$OTHER\|Main.cmx$Clang_LF_LIB$OTHER\|Main.cmx$Msvc_LF_LIB$OTHER"
   1
+
+-std=c++11 is given on OCaml 5.0
+================================
+
+  $ dune clean
+
+  $ dune exec ./cpp11.exe
+  Hi from C++11