objtool: Also include tools/include/uapi

objtool: Also include tools/include/uapi

When building objtool against a sysroot that contains a stripped down
version of the UAPI headers, the following error happens:

    In file included from arch/x86/decode.c:10:
    In file included from .../tools/arch/x86/include/asm/insn.h:10:
    In file included from <sysroot>/include/asm/byteorder.h:9:
    In file included from <sysroot>/include/linux/byteorder/little_endian.h:15:
    In file included from <sysroot>/include/linux/stddef.h:9:
    In file included from .../tools/include/linux/compiler_types.h:36:
    .../tools/include/linux/compiler-gcc.h:3:2: error: "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
        3 | #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
        |  ^
    1 error generated.

As hinted by the error, this is because <sysroot>/include/linux/stddef.h
(a stripped-down version of uapi/include/linux/stddef.h) includes
linux/compiler_types.h directly. However, this gets resolved to
tools/include/linux/compiler_types.h, which is not expected to be
included directly.

To resolve this, I added tools/include/uapi to the include paths when
building objtool. With this trick, linux/stddef.h is resolved to
tools/include/uapi/linux/stddef.h, which doesn't include
linux/compiler_types.h.

Signed-off-by: HONG Yifan <elsk@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>