```cmake
set(PBM_PREFIX protobuf_mutator)
set(PBM_PATH ${CMAKE_CURRENT_BINARY_DIR}/${PBM_PREFIX}/src/${PBM_PREFIX})
set(PBM_LIB_PATH ${PBM_PATH}-build/src/libprotobuf-mutator.a)
set(PBM_FUZZ_LIB_PATH ${PBM_PATH}-build/src/libfuzzer/libprotobuf-mutator-libfuzzer.a)

ExternalProject_Add(${PBM_PREFIX}
  PREFIX ${PBM_PREFIX}
  GIT_REPOSITORY https://github.com/google/libprotobuf-mutator.git
  GIT_TAG master
  CMAKE_ARGS -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
  CMAKE_CACHE_ARGS -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER}
                   -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER}
  BUILD_BYPRODUCTS ${PBM_LIB_PATH} ${PBM_FUZZ_LIB_PATH}
  UPDATE_COMMAND ""
  INSTALL_COMMAND ""
  )

set(ProtobufMutator_INCLUDE_DIRS ${PBM_PATH})
set(ProtobufMutator_LIBRARIES ${PBM_FUZZ_LIB_PATH} ${PBM_LIB_PATH})
```

Include ExternalProject before using it.
user
```cmake
include(ExternalProject)
set(PBM_PREFIX protobuf_mutator)
set(PBM_PATH ${CMAKE_CURRENT_BINARY_DIR}/${PBM_PREFIX}/src/${PBM_PREFIX})
set(PBM_LIB_PATH ${PBM_PATH}-build/src/libprotobuf-mutator.a)
set(PBM_FUZZ_LIB_PATH ${PBM_PATH}-build/src/libfuzzer/libprotobuf-mutator-libfuzzer.a)

ExternalProject_Add(${PBM_PREFIX}
  PREFIX ${PBM_PREFIX}
  GIT_REPOSITORY https://github.com/google/libprotobuf-mutator.git
  GIT_TAG master
  CMAKE_ARGS -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
  CMAKE_CACHE_ARGS -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER}
                   -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER}
  BUILD_BYPRODUCTS ${PBM_LIB_PATH} ${PBM_FUZZ_LIB_PATH}
  UPDATE_COMMAND ""
  INSTALL_COMMAND ""
  )

set(ProtobufMutator_INCLUDE_DIRS ${PBM_PATH})
set(ProtobufMutator_LIBRARIES ${PBM_FUZZ_LIB_PATH} ${PBM_LIB_PATH})
```
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