fix SIGFPE caused by signed division overflow

Avoid evaluating INT_MIN / -1 and INT_MIN % -1, which will trap on x86
and crash sparse.

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Christopher Li <sparse@chrisli.org>
sparse, llvm: fix link errors

This patch fixes the following link errors.

    libLLVMSupport.a(Signals.o): In function `llvm::sys::PrintStackTrace(_IO_FILE*)':
    Signals.inc:269: undefined reference to `dladdr'
    Signals.inc:281: undefined reference to `dladdr'

Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Christopher Li <sparse@chrisli.org>
Trivial: Remove redundant Makefile variable

Signed-off-by: Christopher Li <sparse@chrisli.org>