doc(runtime-c-api) Declare the example as C, so that they are not tested.

Those examples contain C code. They must not be run by `rustdoc` as
tests.

lib/runtime-c-api/src/lib.rs

@@ -1498,7 +1498,8 @@ fn take_last_error() -> Option<Box<Error>> {
 /// bytes needed to store a message.
 ///
 /// # Example
-/// ```
+///
+/// ```c
 /// int error_len = wasmer_last_error_length();
 /// char *error_str = malloc(error_len);
 /// ```
@@ -1517,7 +1518,8 @@ pub extern "C" fn wasmer_last_error_length() -> c_int {
 /// Returns `-1` if an error occurs.
 ///
 /// # Example
-/// ```
+///
+/// ```c
 /// int error_len = wasmer_last_error_length();
 /// char *error_str = malloc(error_len);
 /// wasmer_last_error_message(error_str, error_len);

lib/runtime-c-api/wasmer.h

@@ -417,7 +417,7 @@ wasmer_result_t wasmer_instantiate(wasmer_instance_t **instance,
  * This can be used to dynamically allocate a buffer with the correct number of
  * bytes needed to store a message.
  * # Example
- * ```
+ * ```c
  * int error_len = wasmer_last_error_length();
  * char *error_str = malloc(error_len);
  * ```
@@ -430,7 +430,7 @@ int wasmer_last_error_length(void);
  * Returns the length of the string in bytes.
  * Returns `-1` if an error occurs.
  * # Example
- * ```
+ * ```c
  * int error_len = wasmer_last_error_length();
  * char *error_str = malloc(error_len);
  * wasmer_last_error_message(error_str, error_len);

lib/runtime-c-api/wasmer.hh

@@ -333,7 +333,7 @@ wasmer_result_t wasmer_instantiate(wasmer_instance_t **instance,
 /// This can be used to dynamically allocate a buffer with the correct number of
 /// bytes needed to store a message.
 /// # Example
-/// ```
+/// ```c
 /// int error_len = wasmer_last_error_length();
 /// char *error_str = malloc(error_len);
 /// ```
@@ -344,7 +344,7 @@ int wasmer_last_error_length();
 /// Returns the length of the string in bytes.
 /// Returns `-1` if an error occurs.
 /// # Example
-/// ```
+/// ```c
 /// int error_len = wasmer_last_error_length();
 /// char *error_str = malloc(error_len);
 /// wasmer_last_error_message(error_str, error_len);