clang: Fix warning reg. expansion to 'defined'

Clang produces the following warning. The warning is detailed here:
https://reviews.llvm.org/D15866. Fix the warning.

/home/pranith/devops/code/qemu/hw/display/qxl.c:507:5: warning: macro expansion producing 'defined' has undefined behavior [-Wexpansion-to-defined]
    ^
/home/pranith/devops/code/qemu/include/ui/qemu-spice.h:46:5: note: expanded from macro 'SPICE_NEEDS_SET_MM_TIME'
  (!defined(SPICE_SERVER_VERSION) || (SPICE_SERVER_VERSION < 0xc06))
    ^
/home/pranith/devops/code/qemu/hw/display/qxl.c:1074:5: warning: macro expansion producing 'defined' has undefined behavior [-Wexpansion-to-defined]
    ^
/home/pranith/devops/code/qemu/include/ui/qemu-spice.h:46:5: note: expanded from macro 'SPICE_NEEDS_SET_MM_TIME'
  (!defined(SPICE_SERVER_VERSION) || (SPICE_SERVER_VERSION < 0xc06))

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/ui/qemu-spice.h

@@ -42,8 +42,11 @@ int qemu_spice_set_pw_expire(time_t expires);
 int qemu_spice_migrate_info(const char *hostname, int port, int tls_port,
                             const char *subject);
 
-#define SPICE_NEEDS_SET_MM_TIME                                       \
-  (!defined(SPICE_SERVER_VERSION) || (SPICE_SERVER_VERSION < 0xc06))
+#if !defined(SPICE_SERVER_VERSION) || (SPICE_SERVER_VERSION < 0xc06)
+#define SPICE_NEEDS_SET_MM_TIME 1
+#else
+#define SPICE_NEEDS_SET_MM_TIME 0
+#endif
 
 #if SPICE_SERVER_VERSION >= 0x000c02
 void qemu_spice_register_ports(void);