kernel: Set kernel toolchain roots for aarch64, arm, and x86

The GCC toolchains are no longer added to the path by default, so
we need to hardcode the full paths for these. Also set variables
for every arch, and then set the toolchain to the arch specific var.
This is so we can set the ARM32 cross compile flag for vDSO32
enabled kernels.

Change-Id: I7e099a26a17f4a3cc9be6232a26c671e8fcfbdef

config/BoardConfigKernel.mk

@@ -52,20 +52,28 @@ else
 KERNEL_ARCH := $(TARGET_KERNEL_ARCH)
 endif
 
+GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_OS)-x86
+# arm64 toolchain
+KERNEL_TOOLCHAIN_arm64 := $(GCC_PREBUILTS)/aarch64/aarch64-linux-android-4.9/bin
+KERNEL_TOOLCHAIN_PREFIX_arm64 := aarch64-linux-android-
+# arm toolchain
+KERNEL_TOOLCHAIN_arm := $(GCC_PREBUILTS)/arm/arm-linux-androideabi-4.9/bin
+KERNEL_TOOLCHAIN_PREFIX_arm := arm-linux-androidkernel-
+# x86 toolchain
+KERNEL_TOOLCHAIN_x86 := $(GCC_PREBUILTS)/x86/x86_64-linux-android-4.9/bin
+KERNEL_TOOLCHAIN_PREFIX_x86 := x86_64-linux-android-
+
 TARGET_KERNEL_CROSS_COMPILE_PREFIX := $(strip $(TARGET_KERNEL_CROSS_COMPILE_PREFIX))
 ifneq ($(TARGET_KERNEL_CROSS_COMPILE_PREFIX),)
 KERNEL_TOOLCHAIN_PREFIX ?= $(TARGET_KERNEL_CROSS_COMPILE_PREFIX)
-else ifeq ($(KERNEL_ARCH),arm64)
-KERNEL_TOOLCHAIN_PREFIX ?= aarch64-linux-android-
-else ifeq ($(KERNEL_ARCH),arm)
-KERNEL_TOOLCHAIN_PREFIX ?= arm-linux-androidkernel-
-else ifeq ($(KERNEL_ARCH),x86)
-KERNEL_TOOLCHAIN_PREFIX ?= x86_64-linux-android-
+else
+KERNEL_TOOLCHAIN ?= $(KERNEL_TOOLCHAIN_$(KERNEL_ARCH))
+KERNEL_TOOLCHAIN_PREFIX ?= $(KERNEL_TOOLCHAIN_PREFIX_$(KERNEL_ARCH))
 endif
 
 ifeq ($(KERNEL_TOOLCHAIN),)
 KERNEL_TOOLCHAIN_PATH := $(KERNEL_TOOLCHAIN_PREFIX)
-else ifneq ($(KERNEL_TOOLCHAIN_PREFIX),)
+else
 KERNEL_TOOLCHAIN_PATH := $(KERNEL_TOOLCHAIN)/$(KERNEL_TOOLCHAIN_PREFIX)
 endif
 
@@ -84,7 +92,7 @@ endif
 
 # Needed for CONFIG_COMPAT_VDSO, safe to set for all arm64 builds
 ifeq ($(KERNEL_ARCH),arm64)
-   KERNEL_CROSS_COMPILE += CROSS_COMPILE_ARM32="arm-linux-androideabi-"
+   KERNEL_CROSS_COMPILE += CROSS_COMPILE_ARM32="$(KERNEL_TOOLCHAIN_arm)/$(KERNEL_TOOLCHAIN_PREFIX_arm)"
 endif
 
 # Clear this first to prevent accidental poisoning from env
@@ -133,11 +141,10 @@ endif
 KERNEL_MAKE_CMD := $(BUILD_TOP)/prebuilts/build-tools/$(HOST_OS)-x86/bin/make
 
 # Set the full path to the gcc command
-GCC_PREBUILTS := $(BUILD_TOP)/prebuilts/gcc/$(HOST_OS)-x86/host
 ifeq ($(HOST_OS),darwin)
-KERNEL_HOST_TOOLCHAIN_ROOT := $(GCC_PREBUILTS)/i686-apple-darwin-4.2.1/bin/i686-apple-darwin11-
+KERNEL_HOST_TOOLCHAIN_ROOT := $(GCC_PREBUILTS)/host/i686-apple-darwin-4.2.1/bin/i686-apple-darwin11-
 else
-KERNEL_HOST_TOOLCHAIN_ROOT := $(GCC_PREBUILTS)/x86_64-linux-glibc2.17-4.8/bin/x86_64-linux-
+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++