Disable building with OpenMP on macOS runners.

Building with OpenMP causes some test failures on macOS,
see ElmerCSC#634 (comment).
The affected tests currently are: `H1BasisEvaluation`,
`SD_H1BasisEvaluation`, and `pointload2`.

For the time being, disable building with OpenMP in CI.

The flags that are necessary to build with OpenMP using Homebrew on macOS
are left intact. So, it should be easy to enable runners with OpenMP in
case this issue will be fixed.

Note that the tests with OpenMP fail for optimization level `-O3` but
succeed with `-O2`.

.github/workflows/build-macos-homebrew.yaml

@@ -18,12 +18,24 @@ jobs:
 
     runs-on: ${{ matrix.os }}
 
+    name: ${{ matrix.os }} (${{ matrix.openmp }} OpenMP)
+
     strategy:
       # Allow other runners in the matrix to continue if some fail
       fail-fast: false
 
       matrix:
         os: [macos-14, macos-13]
+        openmp: [without]
+        # Building with OpenMP causes some test failures on macOS.
+        # The affected tests currently are: H1BasisEvaluation,
+        # SD_H1BasisEvaluation, and pointload2.
+        # For the time being, disable building with OpenMP in CI.
+        # FIXME: Consider building with OpenMP when this (potentially
+        # upstrean) issue has been fixed.
+        # include:
+        #   - os: macos-14
+        #     openmp: with
 
     steps:
       - name: get CPU information
@@ -49,7 +61,9 @@ jobs:
           brew install --overwrite python@3.12 python@3.13
           brew reinstall gcc
           brew install \
-            cmake libomp openblas open-mpi suitesparse \
+            cmake \
+            $([ "${{ matrix.openmp }}" == "with" ] && echo "libomp") \
+            openblas open-mpi suitesparse \
             qwt vtk opencascade
           echo "HOMEBREW_PREFIX=$(brew --prefix)" >> $GITHUB_ENV
 
@@ -66,11 +80,12 @@ jobs:
             -DCMAKE_Fortran_COMPILER=gfortran \
             -DCMAKE_INSTALL_PREFIX="${GITHUB_WORKSPACE}/usr" \
             -DBLA_VENDOR="OpenBLAS" \
-            -DCMAKE_PREFIX_PATH="${HOMEBREW_PREFIX}/opt/libomp;${HOMEBREW_PREFIX}/opt/openblas;${HOMEBREW_PREFIX}/opt/qt;${HOMEBREW_PREFIX}/opt/qwt" \
-            -DWITH_OpenMP=ON \
-            -DOpenMP_C_FLAGS="-Xclang -fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include" \
-            -DOpenMP_CXX_FLAGS="-Xclang -fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include" \
-            -DOpenMP_Fortran_FLAGS="-fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include" \
+            -DCMAKE_PREFIX_PATH="$([ "${{ matrix.openmp }}" == "with" ] && echo "${HOMEBREW_PREFIX}/opt/libomp;")${HOMEBREW_PREFIX}/opt/openblas;${HOMEBREW_PREFIX}/opt/qt;${HOMEBREW_PREFIX}/opt/qwt" \
+            $([ "${{ matrix.openmp }}" == "with" ] && \
+              echo "-DWITH_OpenMP=ON \
+                -DOpenMP_C_FLAGS=\"-Xclang -fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include\" \
+                -DOpenMP_CXX_FLAGS=\"-Xclang -fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include\" \
+                -DOpenMP_Fortran_FLAGS=\"-fopenmp -I${HOMEBREW_PREFIX}/opt/libomp/include\"") \
             -DWITH_LUA=ON \
             -DWITH_MPI=ON \
             -DMPI_TEST_MAXPROC=2 \