ANDROID: build.config.common: enable LLVM=1

This moves builds to all use LLVM=1 argument to make, rather than
CC=clang NM=llvm-nm OBJCOPY=llvm-objcopy ... (see also
https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities).

Step 3 of:
https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+/master/BINUTILS_KERNEL_DEPRECATION.md



Bug: 65987925
Bug: 141693040
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: I0d1a4e322a76a91746f2d0888bbba1eee54a7926