==> make
AWK=awk srcdir=. sh ./term.sh
AWK=awk CC="clang -g -O2 -Wall -Wextra -std=c11" srcdir=. sh ./comm.sh
clang -c  -iquote. -DETCSCREENRC='"/usr/local/Cellar/screen/HEAD/etc/screenrc"' -DSCREENENCODINGS='"/usr/local/Cellar/screen/HEAD/share/screen/utf8encodings"' -g -O2 -Wall -Wextra -std=c11 screen.c -o screen.o
screen.c:1594:36: error: no member named 'm_tchars' in 'struct mode'
                        char ibuf = displays->d_OldMode.m_tchars.t_intrc;
                                    ~~~~~~~~~~~~~~~~~~~ ^
1 error generated.
make: * [screen.o] Error 1

There are a few build errors. That is the first. Defining POSIX seems to help with most of them. A patch that lets it build is attached. I couldn't convince configure to define POSIX, so please forgive the repetitive defines.