Switch to the OpenBSD implementations of the wide scanf functions.

This also gets us the C99 wcstoimax and wcstoumax, and a working fgetwc and
ungetwc, all of which are needed in the implementation.

This also brings several other files closer to upstream.

Change-Id: I23b025a8237a6dbb9aa50d2a96765ea729a85579

tests/inttypes_test.cpp

@@ -38,3 +38,11 @@ TEST(inttypes, misc) {
   sscanf(buf, "%08" SCNuPTR, &u);
   sscanf(buf, "%08" SCNxPTR, &u);
 }
+
+TEST(inttypes, wcstoimax) {
+  ASSERT_EQ(123, wcstoimax(L"123", NULL, 10));
+}
+
+TEST(inttypes, wcstoumax) {
+  ASSERT_EQ(123U, wcstoumax(L"123", NULL, 10));
+}