ANDROID: Kbuild, LLVMLinux: allow overriding clang target triple

Android has an unusual setup where the kernel needs to target
[arch]-linux-gnu to avoid Android userspace-specific flags and
optimizations, but AOSP doesn't ship a matching binutils.

Add a new variable CLANG_TRIPLE which can override the "-target" triple
used to compile the kernel, while using a different CROSS_COMPILE to
pick the binutils/gcc installation.  For Android you'd do something
like:

  export CLANG_TRIPLE=aarch64-linux-gnu-
  export CROSS_COMPILE=aarch64-linux-android-

If you don't need something like this, leave CLANG_TRIPLE unset and it
will default to CROSS_COMPILE.

Change-Id: I85d63599c6ab8ed458071cdf9197d85b1f7f150b
Signed-off-by: Greg Hackmann <ghackmann@google.com>

diff --git a/Makefile b/Makefile
index 0d42e9d16812f9e4eadc168cd9aedbb956d53c05..2da4fd0851ccf66e3deecb807ba8c607a68c2199 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -698,7 +698,8 @@ KBUILD_CFLAGS += $(stackp-flag)
 
 ifeq ($(cc-name),clang)
 ifneq ($(CROSS_COMPILE),)
-CLANG_TARGET   := --target=$(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TRIPLE   ?= $(CROSS_COMPILE)
+CLANG_TARGET   := --target=$(notdir $(CLANG_TRIPLE:%-=%))
 GCC_TOOLCHAIN  := $(realpath $(dir $(shell which $(LD)))/..)
 endif
 ifneq ($(GCC_TOOLCHAIN),)