Cleanup: Various clang-tidy warnings in intern

Pull Request: https://projects.blender.org/blender/blender/pulls/133734

intern/utfconv/utf_winfunc.cc

@@ -12,13 +12,13 @@
 
 #include "utf_winfunc.hh"
 #include "utfconv.hh"
+#include <cwchar>
 #include <io.h>
-#include <wchar.h>
 #include <windows.h>
 
 FILE *ufopen(const char *filename, const char *mode)
 {
-  FILE *f = NULL;
+  FILE *f = nullptr;
   UTF16_ENCODE(filename);
   UTF16_ENCODE(mode);
 
@@ -108,7 +108,7 @@ int umkdir(const char *pathname)
 
 char *u_alloc_getenv(const char *varname)
 {
-  char *r = 0;
+  char *r = nullptr;
   wchar_t *str;
   UTF16_ENCODE(varname);
   if (varname_16) {

intern/utfconv/utf_winfunc.hh

@@ -13,7 +13,7 @@
 #  error "This file can only compile on windows"
 #endif
 
-#include <stdio.h>
+#include <cstdio>
 
 FILE *ufopen(const char *filename, const char *mode);
 int uopen(const char *filename, int oflag, int pmode);

intern/utfconv/utfconv.cc

@@ -280,9 +280,9 @@ static void utf_8_cut_end(char *inout8, size_t maxcutpoint)
 char *alloc_utf_8_from_16(const wchar_t *in16, size_t add)
 {
   size_t bsize = count_utf_8_from_16(in16);
-  char *out8 = NULL;
+  char *out8 = nullptr;
   if (!bsize) {
-    return NULL;
+    return nullptr;
   }
   out8 = (char *)malloc(sizeof(char) * (bsize + add));
   conv_utf_16_to_8(in16, out8, bsize);
@@ -292,9 +292,9 @@ char *alloc_utf_8_from_16(const wchar_t *in16, size_t add)
 wchar_t *alloc_utf16_from_8(const char *in8, size_t add)
 {
   size_t bsize = count_utf_16_from_8(in8);
-  wchar_t *out16 = NULL;
+  wchar_t *out16 = nullptr;
   if (!bsize) {
-    return NULL;
+    return nullptr;
   }
   out16 = (wchar_t *)malloc(sizeof(wchar_t) * (bsize + add));
   conv_utf_8_to_16(in8, out16, bsize);

intern/utfconv/utfconv.hh

@@ -9,9 +9,9 @@
 #ifndef __UTFCONV_H__
 #define __UTFCONV_H__
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <wchar.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cwchar>
 
 /**
  * Counts how many bytes is required for future utf-8 string using utf-16