How to use Clang

[diehard2]

I'm trying to build my packages and (at the very least) abseil is not using Clang on Linux. as a first pass I attempted to set my clang compiler as follows

set(ENV{VCPKG_CXX_COMPILER} "/home/dev/build/tools/clang-12.0.1/bin/clang++")
set(ENV{VCPKG_C_COMPILER} "/home/dev/build/tools/clang-12.0.1/bin/clang")

set(CMAKE_TOOLCHAIN_FILE ${CMAKE_CURRENT_SOURCE_DIR}/third_party/vcpkg/scripts/buildsystems/vcpkg.cmake CACHE STRING "Vcpkg toolchain file")

you'll notice that it is in a non-standard location. I did a search and couldn't find any way to do this easily. I tried a few other variation of ways to set the environmental variables. Any help is appreciated