F:\source>build -a AARCH64 -t GCC5 -p Platform\ARM\JunoPkg\ArmJuno.dsc -b RELEASE
Build environment: Windows-10-10.0.18362-SP0
Build start time: 17:07:38, Nov.19 2020

WORKSPACE        = f:\source
PACKAGES_PATH    = f:\source\edk2;f:\source\edk2-platforms
EDK_TOOLS_PATH   = f:\source\edk2\basetools
EDK_TOOLS_BIN    = f:\source\edk2\basetools\bin\win32
CONF_PATH        = f:\source\edk2\conf
PYTHON_COMMAND   = C:\Python37\python.exe


Processing meta-data .
Architecture(s)  = AARCH64
Build target     = RELEASE
Toolchain        = GCC5

Active Platform          = f:\source\edk2-platforms\Platform\ARM\JunoPkg\ArmJuno.dsc
.

build.py...
f:\source\edk2-platforms\Platform\ARM\JunoPkg\ArmJuno.dsc(...): error 4000: Instance of library class [VariablePolicyLib] is not found
        in [f:\source\edk2\MdeModulePkg\Universal\Variable\RuntimeDxe\VariableRuntimeDxe.inf] [AARCH64]
        consumed by module [f:\source\edk2\MdeModulePkg\Universal\Variable\RuntimeDxe\VariableRuntimeDxe.inf]


- Failed -
Build end time: 17:07:40, Nov.19 2020
Build total time: 00:00:02


F:\source>cd edk2