Global vars in modules without functions may be incorrectly processed

[iliya-diyachkov]

We introduced empty kernel test_atomic_fn() in capability-integers.ll to force processing of global variables and passing the test since modules without functions are not processed properly (see #66 ). Probably we need to add a fake function automatically for each module without functions.

Another test without functions is transcoding/global-constant-expression.ll. By the way if I add empty function to it, its compilation fails with "Assertion `!hasDefs || resType || I.getOpcode() == TargetOpcode::G_GLOBAL_VALUE' failed" in SPIRVInstructionSelector.cpp:282. Actually the opcode is G_PTR_ADD which we get after IRTranslator:

  %10:_(p1) = G_PTR_ADD %8:_, %11:anyid(s32)
  %12:_(p1) = COPY %8:_(p1)
  %14:_(p1) = G_GLOBAL_VALUE @k_var
  %22:anyid(s32) = G_INTRINSIC_W_SIDE_EFFECTS intrinsic(@llvm.spv.const.composite), %4:anyid(s8), %4:anyid(s8)
  %23:type(s32) = OpTypeArray %16:type(s32), %18:id(s32)
  %6:anyid(s32) = ASSIGN_TYPE %22:anyid(s32), %23:type(s32)
  G_INTRINSIC_W_SIDE_EFFECTS intrinsic(@llvm.spv.init.global), %8:_(p1), %6:anyid(s32)
  %15:anyid(s32) = G_INTRINSIC_W_SIDE_EFFECTS intrinsic(@llvm.spv.const.composite), %10:_(p1), %12:_(p1)