Split impl_numbers.

The current macro structure is odd, handling the plural case by falling
through the singular cases. This commit splits it in two, making it
simpler and clearer.

Author: nnethercote

crates/spirv-std/src/integer.rs

@@ -18,6 +18,12 @@ pub trait SignedInteger: Integer {}
 pub trait UnsignedInteger: Integer {}
 
 macro_rules! impl_numbers {
+    ($(impl $trait:ident for $typ:ty;)+) => {
+        $(impl_number!(impl $trait for $typ;);)+
+    };
+}
+
+macro_rules! impl_number {
     (impl UnsignedInteger for $typ:ty;) => {
         unsafe impl Integer for $typ {
             const WIDTH: usize = core::mem::size_of::<$typ>() * 8;
@@ -34,10 +40,6 @@ macro_rules! impl_numbers {
 
         impl SignedInteger for $typ {}
     };
-    ($(impl $trait:ident for $typ:ty;)+) => {
-        $(impl_numbers!(impl $trait for $typ;);)+
-    };
-
 }
 
 impl_numbers! {