编译ohos时候，如果需要增量编译则需要使用ccache，如果没有则会有以下提示，安装即可：

sudo apt install ccache

The target_cpu needs to be specified, default target_cpu=arm
[OHOS WARNING] Failed to find ccache, ccache disabled.
[OHOS INFO] root_out_dir=//out/bearpi_hm_nano/bearpi_hm_nano
[OHOS INFO] root_build_dir=//out/bearpi_hm_nano/bearpi_hm_nano
[OHOS INFO] root_gen_dir=//out/bearpi_hm_nano/bearpi_hm_nano/gen
[OHOS INFO] current_toolchain=//build/lite/toolchain:riscv32-unknown-elf
[OHOS INFO] host_toolchain=//build/toolchain/linux:clang_x64