Use armv7a-linux-androideabi for arm device triple.

* This is a workaround of llvm LTO bug.
* Keep using current NDK include directory path.
  NDKTriple is default ClangTriple but kept as GccTriple for arm device.

Bug: 72619014
Test: make checkbuild
Change-Id: I5dc63c99760325c60bc2da98fd6a3125cef7267d

cc/config/arm_device.go

@@ -325,6 +325,12 @@ func (t *toolchainArm) InstructionSetFlags(isa string) (string, error) {
 }
 
 func (t *toolchainArm) ClangTriple() string {
+	// http://b/72619014 work around llvm LTO bug.
+	return "armv7a-linux-androideabi"
+}
+
+func (t *toolchainArm) ndkTriple() string {
+	// Use current NDK include path, while ClangTriple is changed.
 	return t.GccTriple()
 }