libsndfile: add cmake compatibility flag, remove CFLAGS for gcc2

The compatibility flag can be removed again on the next update, it has been
fixed upstream already, but not in a simple patch, hence using the flag for now
instead of backporting the changes.

media-libs/libsndfile/libsndfile-1.2.2.recipe

@@ -81,11 +81,9 @@ BUILD_PREREQUIRES="
 
 BUILD()
 {
-	if [ $effectiveTargetArchitecture = x86_gcc2 ]; then
-		export CFLAGS=-O1
-	fi
 	cmake -B build -S . -DCMAKE_BUILD_TYPE=Release \
 		$cmakeDirArgs \
+		-DCMAKE_POLICY_VERSION_MINIMUM=3.5 \
 		-DBUILD_SHARED_LIBS=ON \
 		-DBUILD_TESTING=OFF \
 		-DBUILD_EXAMPLES=OFF \