Fixing a load of issues related to autoconf and some small source-level issues to re-add clang support.
autoconf feature detection probably needs some addressing - partially as -Werror is applied late.
I really don't know why I tried to do ring-buffers without gaps, the
code complication is just not worth the tiny savings in memory. In fact,
just the switch from pointers to 32-bit offsets saves more memory than
not having gaps (on 64-bit systems, no change on 32-bit).
I've decided that appending to a full single-line buffer should simply
scroll through the existing text. Unsurprisingly, the existing code
doesn't handle the situation all that well. While I've already got a fix
for it, I think I've got a better idea that will handle full buffers
more gracefully.
This fixes the current line object getting corrupted by the tail line
update when the buffer is filled with a single line. There are probably
more tests to write and bugs to fix :)
I was looking through the code for Con_BufferAddText trying to figure
out what it was doing (answer: ring buffer for both text and lines) and
got suspicious about its handling of the line objects. I decided an
automated test was in order. It turns out I was right: filling the
buffer with a single long line causes the tail line to trample the
current line, setting its pointer and length to 0 when the final
character is put in the buffer.
