Add cmake_opts value to allow specifying an alternate toolchain

The new "windows-latest-clang" target does not honor the CXX environment
variable and uses the default MSVC compiler.  This tries to tell cmake to
handle things via a toolset name.

Signed-off-by: Sean Robinson <sean.robinson@scottsdalecc.edu>

.github/workflows/ci.yml

@@ -58,6 +58,7 @@ jobs:
             os: windows-latest
             c_compiler: clang-cl
             cxx_compiler: clang-cl
+            cmake_opts: -T ClangCL
 
     steps:
 
@@ -66,7 +67,7 @@ jobs:
 
     - name: Configure
       working-directory: test
-      run: cmake -S . -B build
+      run: cmake -S . -B build ${{ matrix.cmake_opts }}
       env:
         CC: ${{ matrix.c_compiler }}
         CXX: ${{ matrix.cxx_compiler }}