GLib's doc list all those properties that can be set in the env for cross compilations:

glib_cv_long_long_format=[ll/q/I64]
glib_cv_stack_grows=[yes/no]
glib_cv_working_bcopy=[yes/no]
glib_cv_sane_realloc=[yes/no]
glib_cv_have_strlcpy=[yes/no]
glib_cv_have_qsort_r=[yes/no]
glib_cv_va_val_copy=[yes/no]
glib_cv_rtldglobal_broken=[yes/no]
glib_cv_uscore=[yes/no]
ac_cv_func_posix_getpwuid_r=[yes/no]
ac_cv_func_nonposix_getpwuid_r=[yes/no]
ac_cv_func_posix_getgrgid_r=[yes/no]
glib_cv_use_pid_surrogate=[yes/no]
ac_cv_func_printf_unix98=[yes/no]
ac_cv_func_vsnprintf_c99=[yes/no]

In meson we should use meson.get_cross_property() and document that user can define those variables in cross file's [properties] section.