MdeModulePkg/RegularExpressionDxe: guard the definition of ARRAY_SIZE

In one of the next patches, we'll introduce ARRAY_SIZE in
"MdePkg/Include/Base.h". In order to proceed in small steps, make the
module-local definition of ARRAY_SIZE conditional. This way the
introduction of the macro under MdePkg will silently switch this module
over (after which we can remove the module-local definition completely).

Cc: Cecil Sheng <cecil.sheng@hpe.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Feng Tian <feng.tian@Intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

MdeModulePkg/Universal/RegularExpressionDxe/RegularExpressionDxe.h

@@ -26,7 +26,9 @@
 #include <Library/DebugLib.h>
 #include <Library/BaseLib.h>
 
+#ifndef ARRAY_SIZE
 #define ARRAY_SIZE(Array) (sizeof(Array) / sizeof(*Array))
+#endif
 
 /**
   Checks if the input string matches to the regular expression pattern.