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
diff --git a/config/BoardConfigKernel.mk b/config/BoardConfigKernel.mk
index e7d4660..d4be667 100644
--- a/config/BoardConfigKernel.mk
+++ b/config/BoardConfigKernel.mk
@@ -52,7 +52,10 @@
 KERNEL_ARCH := $(TARGET_KERNEL_ARCH)
 endif
 
-CLANG_PREBUILTS := $(BUILD_TOP)/prebuilts/clang/host/$(HOST_PREBUILT_TAG)/clang-r383902b
+LLVM_RELEASE_VERSION ?= 12.0.7
+LLVM_PREBUILTS_VERSION ?= clang-r416183b1
+
+CLANG_PREBUILTS := $(BUILD_TOP)/prebuilts/clang/host/$(HOST_PREBUILT_TAG)/$(LLVM_PREBUILTS_VERSION)
 GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_PREBUILT_TAG)
 # arm64 toolchain
 KERNEL_TOOLCHAIN_arm64 := $(GCC_PREBUILTS)/aarch64/aarch64-linux-android-4.9/bin