meson: make target endianneess available to Kconfig

Some targets use "default y" for boards to filter out those that require
TCG.  For consistency we are switching all other targets to do the same.
MIPS boards may only be available for big-endian or only for
little-endian emulators, add a symbol so that this can be described
with a "depends on" clause.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -3005,7 +3005,7 @@ foreach target : target_dirs
     }
   endif
 
-  accel_kconfig = []
+  target_kconfig = []
   foreach sym: accelerators
     if sym == 'CONFIG_TCG' or target in accelerator_targets.get(sym, [])
       config_target += { sym: 'y' }
@@ -3015,10 +3015,10 @@ foreach target : target_dirs
       else
         config_target += { 'CONFIG_TCG_BUILTIN': 'y' }
       endif
-      accel_kconfig += [ sym + '=y' ]
+      target_kconfig += [ sym + '=y' ]
     endif
   endforeach
-  if accel_kconfig.length() == 0
+  if target_kconfig.length() == 0
     if default_targets
       continue
     endif
@@ -3078,6 +3078,9 @@ foreach target : target_dirs
                                                configuration: config_target_data)}
 
   if target.endswith('-softmmu')
+    target_kconfig += 'CONFIG_' + config_target['TARGET_ARCH'].to_upper() + '=y'
+    target_kconfig += 'CONFIG_TARGET_BIG_ENDIAN=' + config_target['TARGET_BIG_ENDIAN']
+
     config_input = meson.get_external_property(target, 'default')
     config_devices_mak = target + '-config-devices.mak'
     config_devices_mak = configure_file(
@@ -3088,8 +3091,7 @@ foreach target : target_dirs
       command: [minikconf,
                 get_option('default_devices') ? '--defconfig' : '--allnoconfig',
                 config_devices_mak, '@DEPFILE@', '@INPUT@',
-                host_kconfig, accel_kconfig,
-                'CONFIG_' + config_target['TARGET_ARCH'].to_upper() + '=y'])
+                host_kconfig, target_kconfig])
 
     config_devices_data = configuration_data()
     config_devices = keyval.load(config_devices_mak)

target/Kconfig

@@ -17,3 +17,6 @@ source sh4/Kconfig
 source sparc/Kconfig
 source tricore/Kconfig
 source xtensa/Kconfig
+
+config TARGET_BIG_ENDIAN
+    bool