build: disable wayland if linux/input-event-codes.h isn’t available

The wl_pointer interface defines button argument as “a button code as
defined in the Linux kernel's linux/input-event-codes.h header file,
e.g. BTN_LEFT.”

We could #define these few buttons ourselves, but there is no system to
test it on, so for now let’s disable Wayland support on them.

This is a call to non-Linux system maintainers, please help test this
backend on your system and report issues you find, or even working
state.

wscript

@@ -301,6 +301,10 @@ iconv support use --disable-iconv.",
         'deps': 'os-linux',
         'func': check_statement('sys/vfs.h',
                                 'struct statfs fs; fstatfs(0, &fs); fs.f_namelen')
+    }, {
+        'name': 'linux-input-event-codes',
+        'desc': "Linux's input-event-codes.h",
+        'func': check_cc(header_name=['linux/input-event-codes.h']),
     }, {
         'name' : '--lua',
         'desc' : 'Lua',
@@ -491,7 +495,7 @@ video_output_features = [
     } , {
         'name': '--wayland',
         'desc': 'Wayland',
-        'deps': 'wayland-protocols && wayland-scanner',
+        'deps': 'wayland-protocols && wayland-scanner && linux-input-event-codes',
         'func': check_pkg_config('wayland-client', '>= 1.15.0',
                                  'wayland-cursor', '>= 1.15.0',
                                  'xkbcommon',      '>= 0.3.0'),