custom_target() runs cross executables directly instead of using exe_wrapper

[kanavin]

When cross compiling glib, this snippet in gio/tests/meson.build proved problematic:

    plugin_resources_c = custom_target('plugin-resources.c',
      input : 'test4.gresource.xml',
      output : 'plugin-resources.c',
      command : [glib_compile_resources,
                 compiler_type,
                 '--target=@OUTPUT@',
                 '--sourcedir=' + meson.current_source_dir(),
                 '--internal',
                 '--generate-source',
                 '--c-name', '_g_plugin',
                 '@INPUT@'])

Specifically, 'command', e,g. 'glib-compile-resources' executable in the build tree, will be executed by meson directly, even though it is is a cross-binary that has just been built, and will not run directly (and the fact is known from needs_exe_wrapper set to true, and exe wrapper pointing to qemu). Glib upstream tries to work around this by wrapping the target in 'if meson.can_run_host_binaries()', but that returns 'true' as well (because the wrapper is available), and so the target is attempted - and fails.

I've filed a quick fix for glib: https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3067

but the real issue is probably in meson.