Fix testing examples in documentation

Author: alexcrichton

src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md

@@ -155,7 +155,7 @@ or another engine that supports `wasi-threads` is installed and can be found in
 
 It's recommended to conditionally compile code for this target with:
 
-```
+```text
 #[cfg(all(target_os = "wasi", target_env = "p1", target_feature = "atomics"))]
 ```
 

src/doc/rustc/src/platform-support/wasm32-wasip1.md

@@ -126,7 +126,7 @@ can be tested locally, for example, with:
 
 It's recommended to conditionally compile code for this target with:
 
-```
+```text
 #[cfg(all(target_os = "wasi", target_env = "p1"))]
 ```
 

src/doc/rustc/src/platform-support/wasm32-wasip2.md

@@ -58,6 +58,6 @@ This target is not tested in CI at this time. Locally it can be tested with a
 
 It's recommended to conditionally compile code for this target with:
 
-```
+```text
 #[cfg(all(target_os = "wasi", target_env = "p2"))]
 ```