message: fix build script array expansion
  Summary:
  this is the most portable way according to:
  fixed
diff: @@ -188,7 +188,7 @@ function setup_fmt() {
  -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  -DFMT_DOC=OFF \
  -DFMT_TEST=OFF \
  - "${CMAKE_EXTRA_ARGS[@]}" \
  + ${CMAKE_EXTRA_ARGS[@]+"${CMAKE_EXTRA_ARGS[@]}"} \
  ..
  make -j "$nproc"
  make install
  @@ -251,7 +251,7 @@ function setup_folly() {
  cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  -DCMAKE_PREFIX_PATH="$FOLLY_INSTALL_DIR" \
  -DCMAKE_INSTALL_PREFIX="$FOLLY_INSTALL_DIR" \
  - "${CMAKE_EXTRA_ARGS[@]}" \
  + ${CMAKE_EXTRA_ARGS[@]+"${CMAKE_EXTRA_ARGS[@]}"} \
  ..
  make -j "$nproc"
  make install
  @@ -276,7 +276,7 @@ function setup_fizz() {
  -DBUILD_TESTS=ON \
  -DCMAKE_PREFIX_PATH="$FIZZ_INSTALL_DIR" \
  -DCMAKE_INSTALL_PREFIX="$FIZZ_INSTALL_DIR" \
  - "${CMAKE_EXTRA_ARGS[@]}" \
  + ${CMAKE_EXTRA_ARGS[@]+"${CMAKE_EXTRA_ARGS[@]}"} \
  "$FIZZ_DIR/fizz"
  make -j "$nproc"
  make install
  @@ -312,7 +312,7 @@ function setup_libccp() {
  -DCMAKE_PREFIX_PATH="$LIBCCP_INSTALL_DIR" \
  -DCMAKE_INSTALL_PREFIX="$LIBCCP_INSTALL_DIR" \
  -DCMAKE_CXX_FLAGS=\D__CPLUSPLUS__=1 \
  - "${CMAKE_EXTRA_ARGS[@]}" \
  + ${CMAKE_EXTRA_ARGS[@]+"${CMAKE_EXTRA_ARGS[@]}"} \
  "$LIBCCP_DIR"
  make -j "$nproc"
  make install
  @@ -349,7 +349,7 @@ mvfst_cmake_build_args=(
  -DCMAKE_INSTALL_PREFIX="$MVFST_INSTALL_DIR" \
  -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  -DBUILD_TESTS=On \
  - "${CMAKE_EXTRA_ARGS[@]}" \
  + ${CMAKE_EXTRA_ARGS[@]+"${CMAKE_EXTRA_ARGS[@]}"} \
  )
  if [[ -n "${MVFST_ENABLE_CCP-}" ]]; then
  mvfst_cmake_build_args+=(-DCCP_ENABLED=TRUE)
  