Preserve section GC in split mode

Linked targets inherit section compile and link flags from the static nanobind library. Split targets skip that library and lose the flags.

Apply the same options directly to split targets.

Assisted-by: Codex

Author: burgholzer

cmake/nanobind-config.cmake

@@ -573,6 +573,11 @@ function(nanobind_add_module name)
       ${Python_INCLUDE_DIRS} ${NB_DIR}/include)
     target_compile_features(${name} PRIVATE cxx_std_17)
 
+    if (NOT WIN32 AND NOT APPLE AND NOT AIX)
+      target_compile_options(${name} PRIVATE $<${NB_OPT_SIZE}:-ffunction-sections -fdata-sections>)
+      target_link_options(${name} PRIVATE $<${NB_OPT_SIZE}:-Wl,--gc-sections>)
+    endif()
+
     if (WIN32)
       target_link_libraries(${name} PRIVATE Python::SABIModule)
     endif()