Cleanup: Convert winfunc and utfconv to C++

Basically, the intern/utfconv directory, as well as users of
these headers.

Pull Request: https://projects.blender.org/blender/blender/pulls/113901

intern/utfconv/CMakeLists.txt

@@ -11,9 +11,9 @@ set(INC_SYS
 )
 
 set(SRC
-  utfconv.c
+  utfconv.cc
 
-  utfconv.h
+  utfconv.hh
 )
 
 set(LIB
@@ -24,8 +24,8 @@ set(LIB
 # ... because one day we might want to use it on other platforms.
 if(WIN32)
   list(APPEND SRC
-    utf_winfunc.c
-    utf_winfunc.h
+    utf_winfunc.cc
+    utf_winfunc.hh
   )
 endif()
 

intern/utfconv/utf_winfunc.cc

@@ -10,8 +10,8 @@
 #  define _WIN32_IE 0x0501
 #endif
 
-#include "utf_winfunc.h"
-#include "utfconv.h"
+#include "utf_winfunc.hh"
+#include "utfconv.hh"
 #include <io.h>
 #include <wchar.h>
 #include <windows.h>

intern/utfconv/utfconv.cc

@@ -6,7 +6,7 @@
  * \ingroup intern_utf_conv
  */
 
-#include "utfconv.h"
+#include "utfconv.hh"
 
 size_t count_utf_8_from_16(const wchar_t *string16)
 {

intern/utfconv/utfconv.hh

@@ -13,10 +13,6 @@
 #include <stdlib.h>
 #include <wchar.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * Counts how many bytes is required for future utf-8 string using utf-16
  * \param string16: pointer to working utf-16 string
@@ -90,8 +86,4 @@ wchar_t *alloc_utf16_from_8(const char *in8, size_t add);
   } \
   (void)0
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* __UTFCONV_H__ */