Fixes compiler detection with Wundef (#934)

* Fix doc comment for pool::allocate() (#914)

* Fixes compiler detection with Wunder

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Co-authored-by: Michael K <130953568+kmichaelk@users.noreply.github.com>
Co-authored-by: Rafael Laya <rafaellaya@meta.com>

include/etl/profiles/determine_compiler.h

@@ -79,7 +79,7 @@ SOFTWARE.
     #if defined(__clang__) || defined(__llvm__)
       #define ETL_COMPILER_CLANG
       #define ETL_COMPILER_TYPE_DETECTED
-      #if __AVR__ == 1
+      #if defined(__AVR__) && (__AVR__ == 1)
         #define ETL_CROSS_COMPILING_TO_AVR
       #endif
     #endif