rust: fix cfgs of proc-macro2 for 1.63.0

Replay the configuration that would be computed by build.rs when compiling
on a 1.63.0 compiler.

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

subprojects/packagefiles/proc-macro2-1-rs/meson.build

@@ -15,7 +15,9 @@ _proc_macro2_rs = static_library(
   rust_abi: 'rust',
   rust_args: [
     '--cfg', 'feature="proc-macro"',
-    '--cfg', 'span_locations',
+    '--cfg', 'no_literal_byte_character',
+    '--cfg', 'no_literal_c_string',
+    '--cfg', 'no_source_text',
     '--cfg', 'wrap_proc_macro',
   ],
   dependencies: [