Fixed layout of test/ASTMerge.

As outlined in a previous RFC, the test/ASTMerge/Inputs folder is getting full and the tests are starting to become interdependent. This is undesirable because

- it makes it harder to write new tests
- it makes it harder to figure out at a glance what old tests are doing, and
- it adds the risk of breaking one test while changing a different one, because of the interdependencies.

To fix this, according to the conversation in the RFC, I have changed the layout from

a.c
Inputs/a1.c
Inputs/a2.c

to

a/test.c
a/Inputs/a1.c
a/Inputs/a2.c
for all existing tests. I have also eliminated interdependencies by replicating the input files for each test that uses them.

https://reviews.llvm.org/D26571

llvm-svn: 287129