[CMake] fixup build-petsc.

ChemistryLib/CMakeLists.txt

@@ -13,4 +13,7 @@ generate_export_header(ChemistryLib)
 target_link_libraries(ChemistryLib PUBLIC iphreeqc PRIVATE NumLib spdlog::spdlog)
 
 # See https://github.com/ufz/ogs/pull/2982#issuecomment-641086788
-set_source_files_properties(PhreeqcIO.cpp PROPERTIES SKIP_UNITY_BUILD_INCLUSION TRUE)
+set_source_files_properties(PhreeqcIO.cpp
+    CreateChemicalSolverInterface.cpp
+    PhreeqcKernel.cpp
+    PROPERTIES SKIP_UNITY_BUILD_INCLUSION TRUE)