[ThinLTO] Add debug output to test

Add -debug-only=function-import to get more information for debugging
reverse-iteration bot failure from r337050.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337076 91177308-0d34-0410-b5e6-96231b3b80d8

Author: teresajohnson

test/Transforms/FunctionImport/hotness_based_import2.ll

@@ -9,7 +9,7 @@
 ; with threshold decayed by default 0.7 factor. Test ensures that when we
 ; encounter it again from hot path, we re-enqueue with higher non-decayed
 ; threshold which will allow it to be imported.
-; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=10 -import-hot-multiplier=1.0 -import-cold-multiplier=1.0 -S | FileCheck %s --check-prefix=CHECK
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=10 -import-hot-multiplier=1.0 -import-cold-multiplier=1.0 -S -debug-only=function-import | FileCheck %s --check-prefix=CHECK
 ; CHECK-DAG: define available_externally void @hot()
 ; CHECK-DAG: define available_externally void @calledFromHot()