[clang][IFS][test] GreenDragon and Fuchsia Darwin bot fix: BindArchClass Nest.

[plotfi]

Summary

This is a post commit review. If I can re-implement this in a nicer way I will do an NFC commit.

On Darwin the clang driver does not invoke Driver::BuildActions directly
due to the need to handle Universal apps. Because of this there is a
difference in code path where Driver::BuildUniversalActions is called
instead of Driver::BuildActions. BuildUniversalActions ends up calling
Driver::BuildAction but what it does differently is it takes the driver
actions returned and wraps them each into a BindArchAction.

In Driver::BuildJobs there is a check for '-o' to determine that
multiple files are not specified when passing -o, except for Clang
Interface Stub this need to be an exception as we actually want to write
out multiple files: for every libfoo.so we have a libfoo.ifso sidecar
ifso file, etc. To allow this to happen there is a check for
IfsMergeAction, which is permitted to write out a secondary file. Except
on Darwin, the IfsMergeAction gets wrapped in the BindArchAction by
Driver::BuildUniversalActions so the check fails.

This patch is to look inside a BindArchAction in Driver::BuildJobs to
determine if there is in fact an IfsMergeAction, and if-so (pun intended)
allow the secondary sidecard ifs/ifso file to be written out.

clang/lib/Driver/Driver.cpp

void Driver::BuildJobs(Compilation &C) const {
   // enabled we want to be able to generate the stub file at the same time that
   // we generate the real library/a.out. So when a .o, .so, etc are the output,
   // with clang interface stubs there will also be a .ifs and .ifso at the same
   // location.
   if (FinalOutput) {
     unsigned NumOutputs = 0;
     for (const Action *A : C.getActions())
       if (A->getType() != types::TY_Nothing &&
-          A->getKind() != Action::IfsMergeJobClass)
+          !(A->getKind() == Action::IfsMergeJobClass ||
+            (A->getKind() == Action::BindArchClass && A->getInputs().size() &&
+             A->getInputs().front()->getKind() == Action::IfsMergeJobClass)))
         ++NumOutputs;
 
     if (NumOutputs > 1) {
       Diag(clang::diag::err_drv_output_argument_with_multiple_files);
       FinalOutput = nullptr;
     }
   }