having trouble with XTRA_CFLAGS showing up on AM_CXXFLAGS

[Carnë Draug]

Hi

I've been playing around with our configure and I'm having a problem
that maybe someone can help me with.

I'm adding a flag to XTRA_CFLAGS in our configure script and it seems to
somehow be creeping into AM_CXXFLAGS.  The weird thing is that looking into
the generate Makefiled, it is not there.  However, when I run "make -n", I
see it showing up in AM_CXXFLAGS.

Here's what I've been doing.  I've been adding the following lines to
configure.ac:

    XTRA_CFLAGS="$XTRA_CFLAGS -std=c11"
    XTRA_CXXFLAGS="$XTRA_CXXFLAGS -std=c++11"
    CFLAGS="$CFLAGS -std=c11"
    CXXFLAGS="$CXXFLAGS -std=c++11"

After running configure, everything looks fine, the displayed resume
looks correct.  However, once the build actually starts I get warnings
like:

      GEN      libinterp/octave-value/ov-flt-re-mat.df
    cc1plus: warning: command line option ‘-std=c11’ is valid for
C/ObjC but not for C++

And indeed, running "make -n", I get g++ being called with -std=c11.  For
example, the recipe for octave-value/ov-flt-re-mat.df

    g++ -E -DHAVE_CONFIG_H -I. -I/home/carandraug/dev/octave  \
      -I. [....] \
      -std=c11 -pthread -fopenmp [...] \
      [...]
    mv libinterp/octave-value/ov-flt-re-mat.df-t
libinterp/octave-value/ov-flt-re-mat.df

Anyone can explain me what I'm doing wrong?

Thank you.

Carnë