crt: use errno instead of _set_errno() in wcrtomb.c

For some old CRTs _set_errno() is emulated, while errno is
always available.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-crt/misc/wcrtomb.c

diff --git a/mingw-w64-crt/misc/wcrtomb.c b/mingw-w64-crt/misc/wcrtomb.c
index 09a5f35..552d6bd 100644
--- a/mingw-w64-crt/misc/wcrtomb.c
+++ b/mingw-w64-crt/misc/wcrtomb.c
@@ -26,7 +26,7 @@
 
   /* Detect invalid conversion state */
   if (state != NULL && *state) {
-    _set_errno (EINVAL);
+    errno = EINVAL;
     return (size_t) -1;
   }
 
@@ -71,6 +71,6 @@
   return ret;
 
 eilseq:
-  _set_errno (EILSEQ);
+  errno = EILSEQ;
   return (size_t) -1;
 }