[workflows] Stop using the build-test-llvm-project action (#80580)

This action is really just a wrapper around cmake and ninja. It doesn't
add any value to the builds, and I don't think we need it now that there
are reusable workflows.

(cherry picked from commit d25022bb689b9bf48a24c0ae6c29c1d3c2f32823)

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

@@ -98,14 +98,23 @@ jobs:
           key: ${{ matrix.os }}
           variant: sccache
       - name: Build and Test
-        uses: llvm/actions/build-test-llvm-project@main
         env:
           # Workaround for https://github.com/actions/virtual-environments/issues/5900.
           # This should be a no-op for non-mac OSes
           PKG_CONFIG_PATH: /usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig//12
-        with:
-          cmake_args: '-GNinja -DLLVM_ENABLE_PROJECTS="${{ inputs.projects }}" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON -DLLDB_INCLUDE_TESTS=OFF -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache ${{ inputs.extra_cmake_args }}'
-          build_target: '${{ inputs.build_target }}'
+        shell: bash
+        run: |
+          cmake -G Ninja \
+                -B build \
+                -S llvm \
+                -DLLVM_ENABLE_PROJECTS="${{ inputs.projects }}" \
+                -DCMAKE_BUILD_TYPE=Release \
+                -DLLVM_ENABLE_ASSERTIONS=ON \
+                -DLLDB_INCLUDE_TESTS=OFF \
+                -DCMAKE_C_COMPILER_LAUNCHER=sccache \
+                -DCMAKE_CXX_COMPILER_LAUNCHER=sccache \
+                ${{ inputs.extra_cmake_args }}
+          ninja -C build '${{ inputs.build_target }}'
 
       - name: Build and Test libclc
         if: "!startsWith(matrix.os, 'windows') && contains(inputs.projects, 'libclc')"