[libcxx] [test] Remove UNSUPPORTED markings for mingw issues that no longer are present in CI

libcxx/test/std/language.support/support.runtime/ctime.timespec.compile.pass.cpp

 // UNSUPPORTED: c++03, c++11, c++14
 
 // XFAIL: LIBCXX-AIX-FIXME
 
 // ::timespec_get is provided by the C library, but it's marked as
 // unavailable until macOS 10.15
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx10.{{9|10|11|12|13|14}}
 
-// MinGW used to lack timespec_get, but has got it in newer versions.
-// Mark the test as unsupported for a transition period, to avoid spurious
-// failures when upgrading the precommit testing environment. After
-// the testing environment is upgraded, we could remove the marking altogether.
-// UNSUPPORTED: target={{.+}}-windows-gnu
-
 #include <ctime>
 #include <type_traits>
 
 #ifndef TIME_UTC
 #error TIME_UTC not defined
 #endif
 
 std::timespec tmspec = {};
 static_assert(std::is_same<decltype(std::timespec_get(&tmspec, 0)), int>::value, "");

libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.constr/F.pass.cpp

 
 // class thread
 
 // template <class F, class ...Args> thread(F&& f, Args&&... args);
 
 // UNSUPPORTED: libcpp-has-no-threads
 // UNSUPPORTED: sanitizer-new-delete
 
-// This fails on MinGW when statically linked, if built with Clang 13 or older.
-// (It's fixed in the upcoming Clang 14, by https://reviews.llvm.org/D109651.)
-// Prior to the fix, when statically linked, the unwind info for the two
-// (default and overridden) operator new implementations clash.
-// UNSUPPORTED: target={{.+}}-windows-gnu && !windows-dll && clang-13
-
 #include <thread>
 #include <new>
 #include <atomic>
 #include <cstdlib>
 #include <cassert>
 #include <vector>
 
 #include "test_macros.h"