Don't build MmapDataLoader if sys/mman.h isn't available and we're not on Windows (#12743)

It won't work in this case.

Author: swolchok

extension/data_loader/CMakeLists.txt

@@ -16,6 +16,14 @@ if(NOT EXECUTORCH_ROOT)
   set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../..)
 endif()
 
+include(CheckIncludeFile)
+check_include_file(sys/mman.h ET_HAVE_SYS_MMAN_H)
+
+if(NOT ET_HAVE_SYS_MMAN_H AND NOT WIN32)
+  list(REMOVE_ITEM _extension_data_loader__srcs
+       "extension/data_loader/mmap_data_loader.cpp"
+  )
+endif()
 list(TRANSFORM _extension_data_loader__srcs PREPEND "${EXECUTORCH_ROOT}/")
 add_library(extension_data_loader ${_extension_data_loader__srcs})
 target_link_libraries(extension_data_loader executorch_core)