rust: qemu-api-macros: always process subprojects before dependencies

Avoid looking for Rust dependencies via cmake.

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-api-macros/meson.build

@@ -1,3 +1,7 @@
+subproject('proc-macro2-1-rs', required: true)
+subproject('quote-1-rs', required: true)
+subproject('syn-2-rs', required: true)
+
 quote_dep = dependency('quote-1-rs', native: true)
 syn_dep = dependency('syn-2-rs', native: true)
 proc_macro2_dep = dependency('proc-macro2-1-rs', native: true)