kernel: Use Clang as HOST_{CC,CXX}

GCC was deprecated upstream, so switch to Clang.

Change-Id: I8a6c9d6b763db0055189d83f9037ccb0c50a23ea

config/BoardConfigKernel.mk

@@ -52,6 +52,7 @@ else
 KERNEL_ARCH := $(TARGET_KERNEL_ARCH)
 endif
 
+CLANG_PREBUILTS := $(BUILD_TOP)/prebuilts/clang/host/$(HOST_PREBUILT_TAG)/clang-r383902b
 GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_PREBUILT_TAG)
 # arm64 toolchain
 KERNEL_TOOLCHAIN_arm64 := $(GCC_PREBUILTS)/aarch64/aarch64-linux-android-4.9/bin
@@ -116,9 +117,9 @@ ifeq ($(KERNEL_ARCH),arm64)
 endif
 
 ifeq ($(HOST_OS),darwin)
-  KERNEL_MAKE_FLAGS += HOSTCFLAGS="-I$(BUILD_TOP)/external/elfutils/libelf -I/usr/local/opt/openssl/include -L/usr/local/opt/openssl/lib"
+  KERNEL_MAKE_FLAGS += HOSTCFLAGS="-I$(BUILD_TOP)/external/elfutils/libelf -I/usr/local/opt/openssl/include -fuse-ld=lld" HOSTLDFLAGS="-L/usr/local/opt/openssl/lib -fuse-ld=lld"
 else
-  KERNEL_MAKE_FLAGS += CPATH="/usr/include:/usr/include/x86_64-linux-gnu" HOSTCFLAGS="-L/usr/lib/x86_64-linux-gnu -L/usr/lib64"
+  KERNEL_MAKE_FLAGS += CPATH="/usr/include:/usr/include/x86_64-linux-gnu" HOSTCFLAGS="-fuse-ld=lld" HOSTLDFLAGS="-L/usr/lib/x86_64-linux-gnu -L/usr/lib64 -fuse-ld=lld"
 endif
 
 ifneq ($(TARGET_KERNEL_ADDITIONAL_FLAGS),)
@@ -138,14 +139,9 @@ endif
 # Set use the full path to the make command
 KERNEL_MAKE_CMD := $(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/make
 
-# Set the full path to the gcc command
-ifeq ($(HOST_OS),darwin)
-KERNEL_HOST_TOOLCHAIN_ROOT := $(GCC_PREBUILTS)/host/i686-apple-darwin-4.2.1/bin/i686-apple-darwin11-
-else
-KERNEL_HOST_TOOLCHAIN_ROOT := $(GCC_PREBUILTS)/host/x86_64-linux-glibc2.17-4.8/bin/x86_64-linux-
-endif
-KERNEL_MAKE_FLAGS += HOSTCC=$(KERNEL_HOST_TOOLCHAIN_ROOT)gcc
-KERNEL_MAKE_FLAGS += HOSTCXX=$(KERNEL_HOST_TOOLCHAIN_ROOT)g++
+# Set the full path to the clang command
+KERNEL_MAKE_FLAGS += HOSTCC=$(CLANG_PREBUILTS)/bin/clang
+KERNEL_MAKE_FLAGS += HOSTCXX=$(CLANG_PREBUILTS)/bin/clang++
 
 # Since Linux 4.16, flex and bison are required
 KERNEL_MAKE_FLAGS += LEX=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/flex