[libcxx] [test] Fix the get_weekday test on glibc

[mstorsjo]

Summary

This test feeds in the expected utf8 form of weekdays in various
languages, trying to match what libc++ has gathered internally
from strftime(). On glibc, the ru_RU.UTF-8 representation of the
tested weekday is spelled with upper case, while the existing
test reference is lower case.

[Mordante]

Thanks for this improvement! LGTM!

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_weekday.pass.cpp

 // <locale>
 
 // class time_get_byname<charT, InputIterator>
 
 // iter_type
 // get_weekday(iter_type s, iter_type end, ios_base& str,
 //             ios_base::iostate& err, tm* t) const;
 
-// TODO: investigation needed
-// XFAIL: target={{.*}}-linux-gnu{{.*}}
-
 #include <locale>
 #include <cassert>
 #include "test_macros.h"
 #include "test_iterators.h"
 
 #include "platform_support.h" // locale name macros
 
 typedef cpp17_input_iterator<const char*> I;
std::tm t;
         t = std::tm();
         I i = f.get_weekday(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
         assert(i.base() == in+sizeof(in)/sizeof(in[0])-1);
         assert(t.tm_wday == 1);
         assert(err == std::ios_base::eofbit);
     }
     {
         const my_facet f(LOCALE_ru_RU_UTF_8, 1);
-        const char in[] = "\xD0\xBF\xD0\xBE\xD0\xBD\xD0\xB5"
+        const char in[] =
+#ifdef TEST_HAS_GLIBC
+                          "\xD0\x9F" // Upper case
+#else
+                          "\xD0\xBF" // Lower case
+#endif
+                          "\xD0\xBE\xD0\xBD\xD0\xB5"
                           "\xD0\xB4\xD0\xB5\xD0\xBB\xD1\x8C"
                           "\xD0\xBD\xD0\xB8\xD0\xBA";
         err = std::ios_base::goodbit;
         t = std::tm();
         I i = f.get_weekday(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
         assert(i.base() == in+sizeof(in)/sizeof(in[0])-1);
         assert(t.tm_wday == 1);
         assert(err == std::ios_base::eofbit);