meson: do not check supported TCG architecture if no emulators built

Errors about TCI are pointless if only tools are being built; suppress
them even if the user did not specify --disable-tcg.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/tcg/meson.build

@@ -1,4 +1,4 @@
-if not get_option('tcg').allowed()
+if not have_tcg
    subdir_done()
 endif
 

meson.build

@@ -247,6 +247,8 @@ have_vhost_net_vdpa = have_vhost_vdpa and get_option('vhost_net').allowed()
 have_vhost_net_kernel = have_vhost_kernel and get_option('vhost_net').allowed()
 have_vhost_net = have_vhost_net_kernel or have_vhost_net_user or have_vhost_net_vdpa
 
+have_tcg = get_option('tcg').allowed() and (have_system or have_user)
+
 have_tools = get_option('tools') \
   .disable_auto_if(not have_system) \
   .allowed()
@@ -863,7 +865,7 @@ elif host_os == 'haiku'
             cc.find_library('network'),
             cc.find_library('bsd')]
 elif host_os == 'openbsd'
-  if get_option('tcg').allowed() and target_dirs.length() > 0
+  if have_tcg
     # Disable OpenBSD W^X if available
     emulator_link_args = cc.get_supported_link_arguments('-Wl,-z,wxneeded')
   endif
@@ -904,7 +906,7 @@ if host_os == 'netbsd'
 endif
 
 tcg_arch = host_arch
-if get_option('tcg').allowed()
+if have_tcg
   if host_arch == 'unknown'
     if not get_option('tcg_interpreter')
       error('Unsupported CPU @0@, try --enable-tcg-interpreter'.format(cpu))
@@ -2534,7 +2536,7 @@ config_host_data.set('CONFIG_PIXMAN', pixman.found())
 config_host_data.set('CONFIG_SLIRP', slirp.found())
 config_host_data.set('CONFIG_SNAPPY', snappy.found())
 config_host_data.set('CONFIG_SOLARIS', host_os == 'sunos')
-if get_option('tcg').allowed()
+if have_tcg
   config_host_data.set('CONFIG_TCG', 1)
   config_host_data.set('CONFIG_TCG_INTERPRETER', tcg_arch == 'tci')
 endif
@@ -4959,7 +4961,7 @@ if host_arch == 'unknown'
   message('compile or work on this host CPU. You can help by volunteering')
   message('to maintain it and providing a build host for our continuous')
   message('integration setup.')
-  if get_option('tcg').allowed() and target_dirs.length() > 0
+  if have_tcg
     message()
     message('configure has succeeded and you can continue to build, but')
     message('QEMU will use a slow interpreter to emulate the target CPU.')

tcg/meson.build

@@ -1,4 +1,4 @@
-if not get_option('tcg').allowed()
+if not have_tcg
    subdir_done()
 endif