Add --with-socket-path to configure. GitHub issue 5635 from Alexandre Fiori.

Makefile.am

@@ -15,6 +15,9 @@ AM_CPPFLAGS += @XOPEN_DEFINES@ \
 	-DTMUX_LOCK_CMD='"@DEFAULT_LOCK_CMD@"' \
 	-DTMUX_TERM='"@DEFAULT_TERM@"' \
 	-DTMUX_MOUSE=1
+if HAVE_TMUX_SOCK
+AM_CPPFLAGS += -DTMUX_SOCK='"@TMUX_SOCK@"'
+endif
 
 # Additional object files.
 LDADD = $(LIBOBJS)

configure.ac

@@ -111,6 +111,17 @@ case "x$DEFAULT_TERM" in
 	;;
 esac
 
+# Allow the socket directory list to be set. It is a colon-separated list of
+# directories, tried in order; a leading $ is an environment variable.
+AC_ARG_WITH(
+	socket-path,
+	AS_HELP_STRING(--with-socket-path=PATHS, set socket directory list),
+	[TMUX_SOCK=`echo "$withval" | sed 's/[[$]]/$$/g'`],
+	[TMUX_SOCK=]
+)
+AM_CONDITIONAL(HAVE_TMUX_SOCK, [test "x$TMUX_SOCK" != x])
+AC_SUBST(TMUX_SOCK)
+
 # Do we need fuzzers?
 AM_CONDITIONAL(NEED_FUZZING, test "x$enable_fuzzing" = xyes)