[llvm] [workflows] Use /mnt as the build directory on Linux (PR #80583)

[Aiden Grossman via llvm-commits]

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@@ -104,8 +104,15 @@ jobs:
           PKG_CONFIG_PATH: /usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig//12
         shell: bash
         run: |
+          if [ "${{ runner.os }}" == "Linux" ]; then
+            builddir="/mnt/build/"
+            sudo mkdir -p $builddir
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boomanaiden154 wrote:

Interesting. Approach seems fine to me then.

Would be really nice if Github wouldn't use this weird layout for their hosted runners, but I guess it is what it is.

https://github.com/llvm/llvm-project/pull/80583