[tlbuild] Inappropriate compiler flag for C++

[Paul Vojta]

On Sat, Feb 23, 2019 at 04:14:44PM -0700, Karl Berry wrote:
> Hi Andreas,
> 
>     When I './Build --disable-xdvik' on Linux with gcc/g++ 7.3.0
>     ...
>     cc1plus: warning: command line option '-Wimplicit' ...
> 
> Hmm. From what I can see in m4/kpse-warnings.m4, -Wimplicit should only
> be included in kpse_cv_warning_cxxflags if the output of g++
> -dumpversion matches globs 3.* or 4.[012345].* which is presumably not
> the case for 7.3.0.  I don't understand.
> 
> Can you run sh -vx .../Build/source/configure and look for wimplicit in
> the (voluminous) output and see if you can discern why it is being set?
> 
> Or maybe for some reason the kpse_cv_warning_cflags is being applied,
> rather than cxxflags, though this should not be the case.
> 
> Personally, I just compile with --enable-compiler-warnings=no.
> 
> Best,
> Karl

In texk/dvisvgm/dvisvgm-src/src/Makefile, I find:

| WARNING_CFLAGS = -Wimplicit -Wreturn-type
| ...
| AM_CXXFLAGS = $(WARNING_CFLAGS) -Wnon-virtual-dtor \
|         -Wno-mismatched-tags -I$(dvisvgm_srcdir)/libs/clipper \
|	  [etc.]

I'm also getting warnings of the following sort:

| cc1plus: warning: unrecognized command line option ‘-Wno-mismatched-tags’

--Paul