1. Android build
  - Download original android source code ( android-12.0.0_r26 ) from http://source.android.com   
  ( $repo init -u https://android.googlesource.com/platform/manifest -b android-12.0.0_r26
    $repo sync -cdq -j12 --no-tags
    $repo start android-12.0.0_r26 --all 
  )
  - And, merge the source into the android source code
  - Run following scripts to build android
    a) source build/envsetup.sh
    b) lunch 1
    c) make -j4
  - When you compile the android source code, you have to add google original prebuilt source(toolchain) into the android directory.
  - After build, you can find output at out/target/product/generic

2. Kernel Build  
  - When you compile the kernel source code, you have to add google original "prebuilt" source(toolchain) into the android directory.
  - Run following scripts to build kernel
    a) cd kernel-4.19
    b) mkdir -p out
    c) make -j4 -C ./ O=./out ARCH=arm64 CC=../../prebuilts/clang/host/linux-x86/clang-r383902/bin/clang CLANG_TRIPLE=aarch64-linux-gnu- CROSS_COMPILE=../../prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-androidkernel- LGE_TARGET_PLATFORM=mt6765 LGE_TARGET_DEVICE=mdh50lm LGE_LAMP_DEVICE=yes MTK_DTBO_FEATURE=yes PLATFORM_DTB_NAME=mediatek/mt6765 PROJECT_DTB_NAMES=mediatek/muse6765_64_dh50_s muse6765_64_dh50_s_defconfig 
    d) make -j4 -C ./ O=./out ARCH=arm64 CC=../../prebuilts/clang/host/linux-x86/clang-r383902/bin/clang CLANG_TRIPLE=aarch64-linux-gnu- CROSS_COMPILE=../../prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-androidkernel- LGE_TARGET_PLATFORM=mt6765 LGE_TARGET_DEVICE=mdh50lm LGE_LAMP_DEVICE=yes MTK_DTBO_FEATURE=yes PLATFORM_DTB_NAME=mediatek/mt6765 PROJECT_DTB_NAMES=mediatek/muse6765_64_dh50_s headers_install 
    e) make -j4 -C ./ O=./out ARCH=arm64 CC=../../prebuilts/clang/host/linux-x86/clang-r383902/bin/clang CLANG_TRIPLE=aarch64-linux-gnu- CROSS_COMPILE=../../prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-androidkernel- LGE_TARGET_PLATFORM=mt6765 LGE_TARGET_DEVICE=mdh50lm LGE_LAMP_DEVICE=yes MTK_DTBO_FEATURE=yes PLATFORM_DTB_NAME=mediatek/mt6765 PROJECT_DTB_NAMES=mediatek/muse6765_64_dh50_s 2>&1 | tee build_log_kernel_64bit.txt

* "-j4" : The number, 4, is the number of multiple jobs to be invoked simultaneously. 
- After build, you can find the build image(Image.gz) at out/arch/arm64/boot/ 

