[PATCH v2] configure: better check for the C++ compiler

[Yann E. MORIN]

Hello,

On 2017-03-08 18:23 +0100, Yann E. MORIN spake thusly:
> When a C++ compiler is not found, then AC_PROG_CXX will set CXX to
> 'false'.
> 
> However, we test that we can find $CXX, and indeed false exists in
> the PATH, for virtually all systems we have a chance to be compiled
> on. So we conclude that we do have a C++ compiler, when this is
> clearly wrong.
> 
> Improve our hack by trying to run the C++ compiler with a benign call,
> that should succeed if the CXX is really a C++ compiler: tell it to dump
> its pre-defined macros.
> 
> Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
> Reviewed-by: Peter Hutterer <peter.hutterer at who-t.net>

Ping? ;-)

Regards,
Yann E. MORIN.

> ---
> Changes v1 -> v2:
>   - fix typo in commit log  (Peter)
> 
> ---
> Note: this is not a replacement for the patch I sent earlier [0].
> It is complementary.
> ---
>  configure.ac | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 738d744..8b022c1 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -33,11 +33,11 @@ AM_PROG_AS
>  # check if we have C++ compiler. This is hacky workaround,
>  # for a reason why it is this way see
>  # http://lists.gnu.org/archive/html/bug-autoconf/2010-05/msg00001.html
> -have_cpp_compiler=yes
> -
> -if ! which "$CXX" &>/dev/null; then
> -	have_cpp_compiler=no
> -fi
> +AS_IF([! which "$CXX" &>/dev/null];
> +	[have_cpp_compiler=no],
> +	[AS_IF([! $CXX -dM -E - < /dev/null >/dev/null],
> +		[have_cpp_compiler=no],
> +		[have_cpp_compiler=yes])])
>  
>  AM_CONDITIONAL(ENABLE_CPP_TEST, test "x$have_cpp_compiler" = "xyes")
>  
> -- 
> 2.7.4
> 

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