[KDGDB] Fix build with x86 and x64 MSVC (#5187)

```
gdb_input.c(243): error C4477: '_snprintf' : format string '%p' requires
  an argument of type 'void *', but variadic argument 1 has type 'UINT_PTR'

i386_sup.c(98): error C4090: 'return': different 'const' qualifiers
amd64_sup.c(115): error C4090: 'return': different 'const' qualifiers
```

drivers/base/kdgdb/amd64_sup.c

@@ -30,7 +30,7 @@ static const unsigned char reg_size[] =
 };
 
 static
-void*
+const void*
 ctx_to_reg(CONTEXT* ctx, enum reg_name name)
 {
     switch (name)
@@ -60,12 +60,11 @@ ctx_to_reg(CONTEXT* ctx, enum reg_name name)
         case GS: return &ctx->SegGs;
         case SS: return &ctx->SegSs;
     }
-#undef return_reg
-    return 0;
+    return NULL;
 }
 
 static
-void*
+const void*
 thread_to_reg(PETHREAD Thread, enum reg_name reg_name)
 {
     static const void* NullValue = NULL;
@@ -144,7 +143,7 @@ KDSTATUS
 gdb_send_registers(void)
 {
     CHAR RegisterStr[17];
-    UCHAR* RegisterPtr;
+    const UCHAR* RegisterPtr;
     unsigned short i;
     unsigned short size;
 
@@ -218,7 +217,7 @@ KDSTATUS
 gdb_send_register(void)
 {
     enum reg_name reg_name;
-    void *ptr;
+    const void* ptr;
 
     /* Get the GDB register name (gdb_input = "pXX") */
     reg_name = (hex_value(gdb_input[1]) << 4) | hex_value(gdb_input[2]);

drivers/base/kdgdb/gdb_input.c

@@ -187,10 +187,10 @@ handle_gdb_query(void)
     {
         char gdb_out[64];
 #if MONOPROCESS
-        sprintf(gdb_out, "QC:%"PRIxPTR";",
+        sprintf(gdb_out, "QC:%" PRIxPTR ";",
             handle_to_gdb_tid(PsGetThreadId((PETHREAD)(ULONG_PTR)CurrentStateChange.Thread)));
 #else
-        sprintf(gdb_out, "QC:p%"PRIxPTR".%"PRIxPTR";",
+        sprintf(gdb_out, "QC:p%" PRIxPTR ".%" PRIxPTR ";",
             handle_to_gdb_pid(PsGetThreadProcessId((PETHREAD)(ULONG_PTR)CurrentStateChange.Thread)),
             handle_to_gdb_tid(PsGetThreadId((PETHREAD)(ULONG_PTR)CurrentStateChange.Thread)));
 #endif
@@ -240,9 +240,9 @@ handle_gdb_query(void)
                 PETHREAD Thread = CONTAINING_RECORD(CurrentThreadEntry, ETHREAD, ThreadListEntry);
 
 #if MONOPROCESS
-                _snprintf(gdb_out, 40, ",%p", handle_to_gdb_tid(Thread->Cid.UniqueThread));
+                _snprintf(gdb_out, 40, ",%" PRIxPTR, handle_to_gdb_tid(Thread->Cid.UniqueThread));
 #else
-                _snprintf(gdb_out, 40, ",p%p.%p",
+                _snprintf(gdb_out, 40, ",p%" PRIxPTR ".%" PRIxPTR,
                     handle_to_gdb_pid(Process->UniqueProcessId),
                     handle_to_gdb_tid(Thread->Cid.UniqueThread));
 #endif

drivers/base/kdgdb/i386_sup.c

@@ -20,7 +20,7 @@ enum reg_name
 };
 
 static
-void*
+const void*
 ctx_to_reg(CONTEXT* ctx, enum reg_name name, unsigned short* size)
 {
     /* For general registers: 32bits */
@@ -76,11 +76,11 @@ ctx_to_reg(CONTEXT* ctx, enum reg_name name, unsigned short* size)
         return &ctx->ExtendedRegisters[160 + (name - XMM0)*16];
     case MXCSR: return &ctx->ExtendedRegisters[24];
     }
-    return 0;
+    return NULL;
 }
 
 static
-void*
+const void*
 thread_to_reg(PETHREAD Thread, enum reg_name reg_name, unsigned short* size)
 {
     static const void* NullValue = NULL;
@@ -152,8 +152,8 @@ KDSTATUS
 gdb_send_registers(void)
 {
     CHAR RegisterStr[9];
-    UCHAR* RegisterPtr;
-    unsigned i;
+    const UCHAR* RegisterPtr;
+    unsigned short i;
     unsigned short size;
 
     RegisterStr[8] = '\0';
@@ -223,7 +223,7 @@ KDSTATUS
 gdb_send_register(void)
 {
     enum reg_name reg_name;
-    void *ptr;
+    const void* ptr;
     unsigned short size;
 
     /* Get the GDB register name (gdb_input = "pXX") */