omni: Use $(HOST_PREBUILT_TAG) where possible

Change-Id: If211d23ce72b3404368cd723cbb9ea801e61802c
diff --git a/config/BoardConfigKernel.mk b/config/BoardConfigKernel.mk
index 97ceca7..e332f7c 100644
--- a/config/BoardConfigKernel.mk
+++ b/config/BoardConfigKernel.mk
@@ -52,7 +52,7 @@
 KERNEL_ARCH := $(TARGET_KERNEL_ARCH)
 endif
 
-GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_OS)-x86
+GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_PREBUILT_TAG)
 # arm64 toolchain
 KERNEL_TOOLCHAIN_arm64 := $(GCC_PREBUILTS)/aarch64/aarch64-linux-android-4.9/bin
 KERNEL_TOOLCHAIN_PREFIX_arm64 := aarch64-linux-android-
@@ -131,7 +131,7 @@
 endif
 
 # Set use the full path to the make command
-KERNEL_MAKE_CMD := $(BUILD_TOP)/prebuilts/build-tools/$(HOST_OS)-x86/bin/make
+KERNEL_MAKE_CMD := $(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/make
 
 # Set the full path to the gcc command
 ifeq ($(HOST_OS),darwin)
@@ -143,9 +143,9 @@
 KERNEL_MAKE_FLAGS += HOSTCXX=$(KERNEL_HOST_TOOLCHAIN_ROOT)g++
 
 # Since Linux 4.16, flex and bison are required
-KERNEL_MAKE_FLAGS += LEX=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_OS)-x86/bin/flex
-KERNEL_MAKE_FLAGS += YACC=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_OS)-x86/bin/bison
-KERNEL_MAKE_FLAGS += M4=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_OS)-x86/bin/m4
+KERNEL_MAKE_FLAGS += LEX=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/flex
+KERNEL_MAKE_FLAGS += YACC=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/bison
+KERNEL_MAKE_FLAGS += M4=$(BUILD_TOP)/prebuilts/build-tools/$(HOST_PREBUILT_TAG)/bin/m4
 TOOLS_PATH_OVERRIDE += BISON_PKGDATADIR=$(BUILD_TOP)/prebuilts/build-tools/common/bison
 
 # Set the out dir for the kernel's O= arg