Collapse multiple includes of windows.h

Collapse multiple includes of windows.h
(code refactoring)

* dyn_load.c [MSWIN32 || MSWINCE || CYGWIN32]: Do not define
WIN32_LEAN_AND_MEAN and NOSERVICE macros; do not include windows.h.
* include/private/gc_locks.h [GC_WIN32_THREADS && !USE_PTHREAD_LOCKS]:
Likewise.
* include/private/gc_priv.h [!NO_CLOCK && !BSD_TIME && (MSWIN32
|| MSWINCE || WINXP_USE_PERF_COUNTER)]: Likewise.
* include/private/thread_local_alloc.h [!USE_PTHREAD_SPECIFIC
&& !USE_COMPILER_TLS && !USE_WIN32_COMPILER_TLS && USE_WIN32_SPECIFIC]:
Likewise.
* mallocx.c [MSWINCE]: Likewise.
* misc.c [MSWIN32 || MSWINCE || CYGWIN32 && GC_READ_ENV_FILE]: Likewise.
* os_dep.c [MSWIN32 || MSWINCE || CYGWIN32]: Likewise.
* tests/test.c [MSWIN32 || MSWINCE]: Likewise.
* tools/setjmp_t.c [!OS2 && (MSWIN32 || MSWINCE || CYGWIN32)]: Likewise.
* win32_threads.c [GC_WIN32_THREADS]: Likewise.
* include/private/gc_priv.h [MSWIN32 || MSWINCE || CYGWIN32]
(WIN32_LEAN_AND_MEAN, NOSERVICE): Define macro (before include
windows.h).
* include/private/gc_priv.h [MSWIN32 || MSWINCE || CYGWIN32]: Inclde
windows.h and winbase.h before include gc_locks.h (instead of just
before GC_sysinfo declaration).