omni: Set LLVM release and prebuilts version

This tag are used by default but never set.

-exemple: in core/clang/config.mk

Test: check the HOSTCC path in omniromVarsPlugin (out/soong/soong.variables)

LLVM_PREBUILTS_VERSION is set to the newest version of Google ( https://android.googlesource.com/toolchain/llvm-project )

Change-Id: Ia1538e2b1d47616ebba9e8af836727c5e50d2cb7
1 file changed