Normalize use of BR_DOXYGEN_IGNORE.

Author: Thomas Pornin

inc/bearssl_hash.h

@@ -724,7 +724,7 @@ void br_sha256_update(br_sha256_context *ctx, const void *data, size_t len);
  */
 void br_sha256_out(const br_sha256_context *ctx, void *out);
 
-#if BR_DOXYGEN_IGNORE
+#ifdef BR_DOXYGEN_IGNORE
 /**
  * \brief Save SHA-256 running state.
  *
@@ -742,7 +742,7 @@ uint64_t br_sha256_state(const br_sha256_context *ctx, void *out);
 #define br_sha256_state       br_sha224_state
 #endif
 
-#if BR_DOXYGEN_IGNORE
+#ifdef BR_DOXYGEN_IGNORE
 /**
  * \brief Restore SHA-256 running state.
  *