Fix build error on s390x

[vivkong]

HALT is only defined on i386 and x86_64 with recent changes. This breaks the build on s390x.

[parkera]

We have a few architecture checks across CF but we don't usually check for s390x there. Is neither i386 nor x86_64 defined on that platform?

[vivkong]

i386 and x86_64 are not defined on s390x.

Perhaps instead of doing a check on s390x, we can change the code to check like this?

#if defined(__GNUC__) 
        #if defined(__i386__) || defined(__x86_64__)
          #define HALT do {asm __volatile__("int3"); kill(getpid(), 9); __builtin_unreachable(); } while (0)
        #else
          #define HALT do {__builtin_trap(); kill(getpid(), 9); __builtin_unreachable(); } while (0)
        #endif
    #elif defined(_MSC_VER)
        #define HALT do { DebugBreak(); abort(); __builtin_unreachable(); } while (0)
    #else
        #error Compiler not supported
    #endif

[parkera]

Ok - my main question is, though: what happens on s390x in all of the other places we switch on architecture?

[vivkong]

It looks like there is always a fall back when the architecture is not i386/x86_64 so we can continue on s390x. Need to take a look and see if there's work to be done for s390x in those places. In the mean time, can we please fix this so our s390x build can continue? Thanks.

[parkera]

@swift-ci please test and merge