Fix missing definition causing build issues in ARM-based platforms

This solves build problems for ARM-based platforms while integrating latest release/202008 branch.

Since _SIZEOF_VOIDP_ doesn't get defined without the added changes in this PR, it was causing some other missing type definitions errors in the build.

MdeModulePkg/Universal/RegularExpressionDxe/OnigurumaUefiPort.h

@@ -36,11 +36,11 @@ typedef INTN    intptr_t;
 #define offsetof  OFFSET_OF
 #endif
 
-#ifdef MDE_CPU_IA32
+#if defined (MDE_CPU_IA32) || defined (MDE_CPU_ARM)  // MU_CHANGE
 #define SIZEOF_VOIDP  4
 #endif
 
-#ifdef MDE_CPU_X64
+#if defined (MDE_CPU_X64) || defined (MDE_CPU_AARCH64)   // MU_CHANGE
 #define SIZEOF_VOIDP  8
 #endif