[PATCH]Enforce C++11 as a minimum for building gold [PR30867]

[Tom Tromey]

>>>>> "Tamar" == Tamar Christina <Tamar.Christina@arm.com> writes:

Tamar> --- a/gold/aclocal.m4
Tamar> +++ b/gold/aclocal.m4

>> This macro is already in config/ax_cxx_compile_stdcxx.m4 and you can
>> replace the in-line definition with an m4_include, see the end of
>> gold/aclocal.m4.

Tamar> The inlining was done by autoconf when it regenerated the files.  Same thing as in
Tamar> maintainer mode so how does one prevent it from doing so?  Manually editing the
Tamar> file will trigger errors from the sourceware CI.

I don't actually see the aclocal.m4 change in the tree, instead it just
pulls the macro from config/ already.  So there's nothing to do here.

For gdb, it turns out that we have a local change:

# Local GDB customizations:
#
# - AC_SUBST CXX_DIALECT instead of changing CXX/CXXCPP.

Tom