[workflows] Fix libclc CI tests (llvm#80942)

This was broken by 1a64260.

(cherry picked from commit ab92f62)

Author: tstellar

.github/workflows/llvm-project-tests.yml

@@ -105,14 +105,16 @@ jobs:
           # This should be a no-op for non-mac OSes
           PKG_CONFIG_PATH: /usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig//12
         shell: bash
+        id: build-llvm
         run: |
           if [ "${{ runner.os }}" == "Linux" ]; then
             builddir="/mnt/build/"
             sudo mkdir -p $builddir
             sudo chown `whoami`:`whoami` $builddir
           else
-            builddir=build
+            builddir="$(pwd)"/build
           fi
+          echo "llvm-builddir=$builddir" >> "$GITHUB_OUTPUT"
           cmake -G Ninja \
                 -B "$builddir" \
                 -S llvm \
@@ -127,9 +129,11 @@ jobs:
 
       - name: Build and Test libclc
         if: "!startsWith(matrix.os, 'windows') && contains(inputs.projects, 'libclc')"
+        env:
+          LLVM_BUILDDIR: ${{ steps.build-llvm.outputs.llvm-builddir }}
         run: |
           # Make sure all of LLVM libraries that llvm-config needs are built.
-          ninja -C build
-          cmake -G Ninja -S libclc -B libclc-build -DLLVM_DIR="$(pwd)"/build/lib/cmake/llvm -DLIBCLC_TARGETS_TO_BUILD="amdgcn--;amdgcn--amdhsa;r600--;nvptx--;nvptx64--;nvptx--nvidiacl;nvptx64--nvidiacl"
+          ninja -C "$LLVM_BUILDDIR"
+          cmake -G Ninja -S libclc -B libclc-build -DLLVM_DIR="$LLVM_BUILDDIR"/lib/cmake/llvm -DLIBCLC_TARGETS_TO_BUILD="amdgcn--;amdgcn--amdhsa;r600--;nvptx--;nvptx64--;nvptx--nvidiacl;nvptx64--nvidiacl"
           ninja -C libclc-build
           ninja -C libclc-build test