The version of Eigen3 shipped with debian11 is not compatible with libc++-13

debian-11/toolchains/clang-13-20-libcxx

@@ -9,6 +9,9 @@ TOOLCHAIN_CMAKE_FLAGS="-DCMAKE_CXX_STANDARD=20"
 # The GMP library is incompatible with libc++ since compiled with libstdc++
 TOOLCHAIN_CMAKE_FLAGS+=" -DCMAKE_DISABLE_FIND_PACKAGE_GMP:BOOL=TRUE"
 
+# The version of Eigen3 shipped in debian11 is not compatible with clang13
+TOOLCHAIN_CMAKE_FLAGS+=" -DCMAKE_DISABLE_FIND_PACKAGE_Eigen3=1 "
+
 # see base-common/dune.opts: disable CPU detection for Vc library;
 # sadly clang has problems with the setting in dune.opts...
 TOOLCHAIN_CMAKE_FLAGS+=" -DTARGET_ARCHITECTURE=none"