[llvm] [Premerge] Add flang-rt (PR #128678)

[Michael Kruse via llvm-commits]

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@@ -47,6 +48,7 @@ function compute-projects-to-test() {
       # Flang is not stable in Windows CI at the moment
       if [[ $isForWindows == 0 ]]; then
         echo flang
+        echo flang-rt
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Meinersbur wrote:

You are correct, the path to Flang must be passed to the runtimes build. Thanks for noticing.

I have not tested it locally yet. There are some reasons for that
1. I  was assuming that the premerge-monolithic-linux builder (which I tested, see https://github.com/llvm/llvm-zorg/pull/396) was resembling the premerge configuration (which is a bootstrapping build), as was alluded to by a comment.
2. I don't have a local BuildKite infrastructure
3. I was hoping that the pre-merge check of this PR was testing it. While it was in draft mode, it did not show errors.
4. The configuration makes use of a Google-proprietary extensions, such as "-gmlt"

I will try to make it run locally anyway.

https://github.com/llvm/llvm-project/pull/128678