package/tmux: fix BR2_SHARED_STATIC_LIBS

tmux uses custom --enable-static option to drive whether a static link
should be attempted, which is not what the standard libtool directive
is about and that we pass in our autotools-package infra.

This results in the following build failure with systemd or utf8proc
raised since commits 1f618aa388535181c281c85e2b5264532de4ef0f and
e279599d255a79c08ef20b97b96eb248689d52a9:

checking for utf8proc.h... yes
checking for library containing utf8proc_charwidth... no
configure: error: "utf8proc not found"

In file included from tmux.h:34,
                 from alerts.c:23:
compat.h:379:18: error: conflicting types for 'forkpty'; have 'pid_t(int *, char *, struct termios *, struct winsize *)' {aka 'int(int *, char *, struct termios *, struct winsize *)'}
  379 | pid_t            forkpty(int *, char *, struct termios *, struct winsize *);
      |                  ^~~~~~~

Link to (closed) upstream issue:
https://github.com/tmux/tmux/issues/3290

Fixes:
 - http://autobuild.buildroot.org/results/6e8523d8d514bf6d8fc3377d05e5edbe7fc2d5bb
 - http://autobuild.buildroot.org/results/cba06f3bb6d9be25e91f56c390a70ddf9904832e

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/tmux/tmux.mk

@@ -25,6 +25,12 @@ else
 TMUX_CONF_OPTS += --disable-utf8proc
 endif
 
+# tmux uses custom --enable-static option, instead of standard libtool
+# directive resulting in a build failure with systemd or utf8proc
+ifeq ($(BR2_SHARED_STATIC_LIBS),y)
+TMUX_CONF_OPTS += --disable-static
+endif
+
 # Add /usr/bin/tmux to /etc/shells otherwise some login tools like dropbear
 # can reject the user connection. See man shells.
 define TMUX_ADD_TMUX_TO_SHELLS