[rs] Allow concat in SpirV macro

The `include_spirv` macros was set to accept literals only.
Unfortunately, this means that other macros, such as `concat` and `env`
aren't accepted, making it unusable with build script-compiled shaders.
This change allows those macros to be used to load the SpirV at the
expense of a potentially less helpful error message as the `literal`
requirement is differed to the `include_bytes` invocation.

wgpu/src/macros.rs

@@ -143,7 +143,7 @@ fn test_vertex_attr_array() {
 /// It ensure the word alignment as well as the magic number.
 #[macro_export]
 macro_rules! include_spirv {
-    ($path:literal) => {
+    ($path:expr) => {
         $crate::util::make_spirv(&$crate::util::WordAligned(*include_bytes!($path)).0)
     };
 }