As described in the comment, it is not ideal to set CXX/CC.
CONFOPTS=" \
-D CMAKE_BUILD_TYPE=DebugRelease \
-D DEAL_II_WITH_MPI:BOOL=ON \
+-D MPI_CXX_COMPILER=${CXX} \
+-D MPI_C_COMPILER=${CC} \
-D DEAL_II_COMPONENT_DOCUMENTATION:BOOL=OFF \
-D DEAL_II_WITH_LAPACK:BOOL=ON \
-D DEAL_II_WITH_UMFPACK:BOOL=ON \
CONFOPTS="${CONFOPTS} \
${DEAL_II_CONFOPTS}"
+# Disable CXX, CC for deal.II as recommended in
+# https://github.com/dealii/dealii/issues/11478 . Note the we are
+# setting the MPI_*_COMPILER cmake variables above.
+unset CXX
+unset CC
################################################################################
# Check if we hit cmake-3.10+ and deal.II v8.5.1 configure error (MPI / FindMPI)
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