CI: Enable UBSAN for on-target tests

Note that until UBSAN is made deadly by default in LibSanitizer, UBSAN
warnings will not fail the build.

Also remove BUILD_LAGOM=ON from the NORMAL_DEBUG build as it's
unnecessary and extends the build time for no benefit when building with
sanitizers

.github/workflows/cmake.yml

@@ -117,12 +117,12 @@ jobs:
       if: ${{ matrix.debug-options == 'ALL_DEBUG' }}
     - name: Create build environment
       working-directory: ${{ github.workspace }}
-      # Note that this needs to run *even if* the Toolchain was built,
-      # in order to set options like BUILD_LAGOM.
+      # Note that we do not set BUILD_LAGOM for the normal debug build
+      # We build and run the Lagom tests in a separate job, and sanitizer builds take a good while longer than non-sanitized.
       run: |
         mkdir -p Build
         cd Build
-        cmake .. -GNinja -DBUILD_LAGOM=ON -DENABLE_PCI_IDS_DOWNLOAD=OFF -DCMAKE_C_COMPILER=gcc-10 -DCMAKE_CXX_COMPILER=g++-10
+        cmake .. -GNinja -DENABLE_UNDEFINED_SANITIZER=ON -DENABLE_PCI_IDS_DOWNLOAD=OFF -DCMAKE_C_COMPILER=gcc-10 -DCMAKE_CXX_COMPILER=g++-10
       if: ${{ matrix.debug-options == 'NORMAL_DEBUG' }}
 
     # === ACTUALLY BUILD ===