message: build: enable -Wdocumentation if suppressing external warnings
diff: @@ -437,6 +437,10 @@ if test "x$enable_werror" = "xyes"; then
  [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
  AX_CHECK_COMPILE_FLAG([-Werror=unreachable-code-loop-increment],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=unreachable-code-loop-increment"],,[[$CXXFLAG_WERROR]])
  AX_CHECK_COMPILE_FLAG([-Werror=mismatched-tags], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=mismatched-tags"], [], [$CXXFLAG_WERROR])
  +
  + if test x$suppress_external_warnings != xno ; then
  + AX_CHECK_COMPILE_FLAG([-Werror=documentation],[ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Werror=documentation"],,[[$CXXFLAG_WERROR]])
  + fi
  fi
  if test "x$CXXFLAGS_overridden" = "xno"; then
  @@ -464,6 +468,10 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
  [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
  AX_CHECK_COMPILE_FLAG([-Wunreachable-code-loop-increment],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wunreachable-code-loop-increment"],,[[$CXXFLAG_WERROR]])
  + if test x$suppress_external_warnings != xno ; then
  + AX_CHECK_COMPILE_FLAG([-Wdocumentation],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wdocumentation"],,[[$CXXFLAG_WERROR]])
  + fi
  +
  dnl Some compilers (gcc) ignore unknown -Wno-* options, but warn about all
  dnl unknown options if any other warning is produced. Test the -Wfoo case, and
  dnl set the -Wno-foo case if it works.
  