workflows: Fix libclc tests

libclc requires using cmake files to detect the LLVM installation instead
of llvm-config so we need to update our cmake invocation.

Reviewed By: thieta

Differential Revision: https://reviews.llvm.org/D142716

(cherry picked from commit 683b83a)

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

@@ -90,6 +90,6 @@ jobs:
         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_CONFIG=`pwd`/build/bin/llvm-config -DLIBCLC_TARGETS_TO_BUILD="amdgcn--;amdgcn--amdhsa;r600--;nvptx--;nvptx64--;nvptx--nvidiacl;nvptx64--nvidiacl"
+          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 libclc-build
           ninja -C libclc-build test