new objtool unreachable instruction warnings

[Arnd Bergmann]

I only saw these warnings once, they are either very rare, or were introduced
recently:

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

I see this with gcc-4.6 though gcc-7, but not with gcc-4.3.

The configuration file that triggered it is
https://pastebin.com/aMn45GYP

I managed to trace the problem down to the CC_HAVE_ASM_GOTO
macro, without that, we don't run into the problem.

       Arnd