cmake: propagate CMAKE_BUILD_TYPE for ProtobufMutator

Follows-up #4823

NO_CHANGELOG=internal
NO_DOC=internal
NO_TEST=internal

(cherry picked from commit 95d62cfc)

cmake/ProtobufMutator.cmake

@@ -71,7 +71,7 @@ ExternalProject_Add(${LPM_TARGET}
   CONFIGURE_COMMAND ${CMAKE_COMMAND} ${LPM_INSTALL_DIR}/src/${LPM_TARGET}
         -G${CMAKE_GENERATOR}
         -DCMAKE_INSTALL_PREFIX=${LPM_INSTALL_DIR}
-        -DCMAKE_BUILD_TYPE=Debug
+        -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
         -DCMAKE_POSITION_INDEPENDENT_CODE=ON
         -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER}
         -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER}