CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS should export symbols from external objects
This change adds objects files generated by outside sources (e.g. ADD_CUSTOM_COMMAND) to objects.txt, used to generate exported symbols for a dll.
A simple minimal example:
SET( CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON )
ADD_CUSTOM_COMMAND( OUTPUT "C:/foo/bar/lib1.obj" COMMAND ... )
ADD_LIBRARY( someDll SHARED lib2.cpp "C:/foo/bar/lib1.obj" )
ADD_EXECUTABLE( mainEx main.cpp )
TARGET_LINK_LIBRARIES( mainEx someDll )
Where main.cpp depends on a symbol defined in lib1.obj