[cmake] optionally prevent linking python lib

this is necessary for manylinux toolchains where there's no
linkable libpython

CMakeLists.txt

@@ -82,7 +82,9 @@ elseif(APPLE)
   target_link_libraries(dunepybindximodule INTERFACE "-undefined dynamic_lookup")
 endif()
 
-target_link_libraries(dunepybindxiembed INTERFACE pybind11::pybind11 $<BUILD_INTERFACE:${PYTHON_LIBRARIES}>)
+if(NOT DXT_DONT_LINK_PYTHON_LIB)
+  target_link_libraries(dunepybindxiembed INTERFACE pybind11::pybind11 $<BUILD_INTERFACE:${PYTHON_LIBRARIES}>)
+endif()
 add_library(pybind11::embed ALIAS dunepybindxiembed)
 target_link_libraries(dunepybindxi dunepybindxiembed)
 

cmake/modules/DunePybindxiUtils.cmake

@@ -148,7 +148,7 @@ function(dune_pybindxi_add_module target_name)
   set_target_properties(${target_name} PROPERTIES CXX_VISIBILITY_PRESET "hidden")
   set_target_properties(${target_name} PROPERTIES VISIBILITY_INLINES_HIDDEN TRUE)
 
-  if(WIN32 OR CYGWIN)
+  if(NOT DXT_DONT_LINK_PYTHON_LIB AND (WIN32 OR CYGWIN))
     # Link against the Python shared library on Windows
     target_link_libraries(${target_name} ${PYTHON_LIBRARIES})
   elseif(APPLE)