gnumake.h (GMK_EXPORT) [_WIN32]: Move the dllexport declaration
here from makeint.h.
makeint.h (GMK_BUILDING_MAKE) [WINDOWS32]: Define before
including gnumake.h.
load.c (load_object, load_file): Accept an additional argument
DLP and return in it a pointer that can be used to unload the
dynamic object.
read.c (eval): Call load_file with an additional argument, and
record the pointer returned there in the 'struct file' object of
dynamic objects in that object's 'struct file'.
commands.c (execute_file_commands): Unload dynamic objects
before remaking them, to avoid failure to remake if the OS doesn't
allow overwriting objects that are in use.
filedef.h (struct file): New member dlopen_ptr.
gnumake.h (GMK_EXPORT): Define to dllexport/dllimport
decorations for Windows and to nothing on other platforms.
(gmk_eval, gmk_expand, gmk_add_function): Add GMK_EXPORT qualifier
to prototypes.
makeint.h (MAIN): Define before including gnumake.h, to give
correct dllexport decorations to exported functions.
(load_file): Adjust prototype.
loadapi.c: Don't include gnumake.h, since makeint.h already
includes it, and takes care of defining MAIN before doing so.
build_w32.bat (LinkGCC): Produce an import library for functions
exported by Make for loadable dynamic objects.
w32/compat/posixfcn.c (dlclose): New function.
w32/include/dlfcn.h (dlclose): Add prototype.
scripts/features/load: Fix signatures of testload_gmk_setup and
explicit_setup, to bring them in line with the documentation.
Provide a simple API for loaded objects to interact with GNU make. I still
won't guarantee that this API won't change but it's much closer to something
that's supported and provides easy-to-use interfaces with a public header
file.
