[unittests] Add missing includes

[zeroomega]

There are missing include and using in TextStubTests and AsmPrinterDwarfTest and they causes build failures when using vanilla GoogleTest v1.14.0. This patch fixes this issue.

[zeroomega]

First time try Github pull request workflow. I hope I done it correctly.

I have a working draft GoogleTest v1.14.0 roll locally when building/testing LLVM under Linux x64. I still need to clean up the code a bit and validate on a few more platforms before I submit it for review.

The "llvm/ADT/SmallString.h" was included in LLVM's patch to GTest header, so it was implicitly included by the test when using LLVM's GTest fork. This causes problem when using a relatively vanilla GTest.

The missing "using testing::DoAll" is a bit puzzling. I am not sure why the build passed without it currently. It causes build failure when using GTest v1.14.0 and I think we should add it.

[pogo59]

I see only two places that use DoAll in llvm/unittests, and the other one has the using clause, so it makes sense to have it here.

TextStubHelpers.h looks like it doesn't use SmallString, so that include should go in the files where it's actually needed.

[zeroomega]

I see only two places that use DoAll in llvm/unittests, and the other one has the using clause, so it makes sense to have it here.

TextStubHelpers.h looks like it doesn't use SmallString, so that include should go in the files where it's actually needed.

The SmallString is used in files from TextStubV1Tests.cpp to TextStubV5Tests.cpp under the same directory of TextStubHelpers.h, for example: https://github.com/llvm/llvm-project/blob/main/llvm/unittests/TextAPI/TextStubV1Tests.cpp . So I think it may be better to add the missing header in the TextStubHelpers.h, which is shared across these unit tests.

[pogo59]

Hmmm normally the project prefers to minimize dependencies, pushing them down into .cpp files rather than up into .h files. But I see that MemoryBuffer.h is included by TextStubHelpers.h even though it's not used there, so in this case I accept that it's reasonable to put SmallString in the .h file.

LGTM