bug#32032: 26.1; Emacs 26 opens under X with blank window

[gnu_lists]

Given that there are known bugs with this feature that no one is

working on, perhaps we should introduce an optional configure switch

to build without double-buffering.

Agreed. Does it make sense for a Emacs source code newbie to chip in here?

Of course.  We were all newbies at some point.

I created a new `configure.ac` (see https://gist.github.com/halloleo/8f4ba4b1ffcc3874a2ee0e16e03f6618) which provides a `--without-backbuffer` option:

    ./configure --without-gnutls --without-backbuffer

then builds an Emacs exe which starts up properly on unbuffered X servers without any custom `.emacs` file.

Where do I put the `configure.ac` file and how do I create a pull request for it?