Fix a conflict with the Windows header files

In one of the Windows system header files, an "interface" macro is
defined as:

  #define interface struct

This results in some very strange build errors when also including the
descriptor-private.h header file. That's because the dc_usb_params_t
struct has a member field named "interface":

  typedef struct dc_usb_params_t {
      unsigned int interface;
      unsigned char endpoint_in;
      unsigned char endpoint_out;
  } dc_usb_params_t;

As a workaround, define the WIN32_LEAN_AND_MEAN macro before including
the windows.h header file. This excludes some less common Windows API
declarations, including the above one.

src/context.c

@@ -29,6 +29,7 @@
 #include <string.h>
 
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #include <windows.h>
 #endif

src/serial_win32.c

@@ -21,6 +21,7 @@
 
 #include <stdlib.h>
 
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #include <windows.h>
 

src/socket.h

@@ -23,6 +23,7 @@
 #define DC_SOCKET_H
 
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #include <winsock2.h>
 #include <windows.h>

src/timer.c

@@ -26,6 +26,7 @@
 #include <stdlib.h>
 
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #include <windows.h>
 #else

src/usb.c

@@ -28,6 +28,7 @@
 
 #ifdef HAVE_LIBUSB
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #endif
 #include <libusb.h>

src/usbhid.c

@@ -29,6 +29,7 @@
 #include <pthread.h>
 #endif
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #include <windows.h>
 #endif
@@ -43,6 +44,7 @@
 
 #if defined(USE_LIBUSB)
 #ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
 #define NOGDI
 #endif
 #include <libusb.h>