message: build: update ax_cxx_compile_stdcxx to serial 4
diff: # DESCRIPTION
  #
  # Check for baseline language coverage in the compiler for the specified
  -# version of the C++ standard. If necessary, add switches to CXXFLAGS to
  -# enable support. VERSION may be '11' (for the C++11 standard) or '14'
  -# (for the C++14 standard).
  +# version of the C++ standard. If necessary, add switches to CXX and
  +# CXXCPP to enable support. VERSION may be '11' (for the C++11 standard)
  +# or '14' (for the C++14 standard).
  #
  # The second argument, if specified, indicates whether you insist on an
  # extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
  # and this notice are preserved. This file is offered as-is, without any
  # warranty.
  -#serial 1
  +#serial 4
  dnl This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
  dnl (serial version number 13).
  @@ -74,14 +74,17 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
  cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
  AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
  $cachevar,
  - [ac_save_CXXFLAGS="$CXXFLAGS"
  - CXXFLAGS="$CXXFLAGS $switch"
  + [ac_save_CXX="$CXX"
  + CXX="$CXX $switch"
  AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
  [eval $cachevar=yes],
  [eval $cachevar=no])
  - CXXFLAGS="$ac_save_CXXFLAGS"])
  + CXX="$ac_save_CXX"])
  if eval test x\$$cachevar = xyes; then
  - CXXFLAGS="$CXXFLAGS $switch"
  + CXX="$CXX $switch"
  + if test -n "$CXXCPP" ; then
  + CXXCPP="$CXXCPP $switch"
  + fi
  ac_success=yes
  break
  fi
  @@ -97,14 +100,17 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
  cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
  AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
  $cachevar,
  - [ac_save_CXXFLAGS="$CXXFLAGS"
  - CXXFLAGS="$CXXFLAGS $switch"
  + [ac_save_CXX="$CXX"
  + CXX="$CXX $switch"
  AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
  [eval $cachevar=yes],
  [eval $cachevar=no])
  - CXXFLAGS="$ac_save_CXXFLAGS"])
  + CXX="$ac_save_CXX"])
  if eval test x\$$cachevar = xyes; then
  - CXXFLAGS="$CXXFLAGS $switch"
  + CXX="$CXX $switch"
  + if test -n "$CXXCPP" ; then
  + CXXCPP="$CXXCPP $switch"
  + fi
  ac_success=yes
  break
  fi
  @@ -115,7 +121,7 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
  if test x$ac_success = xno; then
  AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
  fi
  - else
  + fi
  if test x$ac_success = xno; then
  HAVE_CXX$1=0
  AC_MSG_NOTICE([No compiler with C++$1 support was found])
  @@ -124,9 +130,7 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
  AC_DEFINE(HAVE_CXX$1,1,
  [define if the compiler supports basic C++$1 syntax])
  fi
  -
  AC_SUBST(HAVE_CXX$1)
  - fi
  ])
  