objtool: Skip unreachable warnings for 'alt' instructions

objtool: Skip unreachable warnings for 'alt' instructions

When a whitelisted function uses one of the ALTERNATIVE macros, it
produces false positive warnings like:

  arch/x86/kvm/vmx.o: warning: objtool: .altinstr_replacement+0x0: unreachable instruction
  arch/x86/kvm/svm.o: warning: objtool: .altinstr_replacement+0x6e: unreachable instruction

There's no easy way to whitelist alternative instructions, so instead
just skip any 'unreachable' warnings associated with them.

Reported-by: Arnd Bergmann <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/a5d0a8c60155f03b36a31fac871e12cf75f35fd0.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>