Update docs with powers-of-two

Author: calebzulawski

compiler/rustc_error_codes/src/error_codes/E0074.md

@@ -11,7 +11,7 @@ This will cause an error:
 #![feature(repr_simd)]
 
 #[repr(simd)]
-struct Bad<T>(T, T, T);
+struct Bad<T>(T, T, T, T);
 ```
 
 This will not:
@@ -20,5 +20,5 @@ This will not:
 #![feature(repr_simd)]
 
 #[repr(simd)]
-struct Good(u32, u32, u32);
+struct Good(u32, u32, u32, u32);
 ```

compiler/rustc_error_codes/src/error_codes/E0076.md

@@ -7,7 +7,7 @@ Erroneous code example:
 #![feature(repr_simd)]
 
 #[repr(simd)]
-struct Bad(u16, u32, u32); // error!
+struct Bad(u16, u32, u32 u32); // error!
 ```
 
 When using the `#[simd]` attribute to automatically use SIMD operations in tuple
@@ -20,5 +20,5 @@ Fixed example:
 #![feature(repr_simd)]
 
 #[repr(simd)]
-struct Good(u32, u32, u32); // ok!
+struct Good(u32, u32, u32, u32); // ok!
 ```

compiler/rustc_error_codes/src/error_codes/E0077.md

@@ -19,5 +19,5 @@ Fixed example:
 #![feature(repr_simd)]
 
 #[repr(simd)]
-struct Good(u32, u32, u32); // ok!
+struct Good(u32, u32, u32, u32); // ok!
 ```