[SystemZ][z/OS] Fix warning caused by umask returning a signed integer type

[abhina.sreeskantharajan]

Summary

On z/OS, umask() returns an int because mode_t is type int, however it is being compared to an unsigned int. This patch fixes the following warning we see when compiling Path.cpp.

comparison of integers of different signs: 'const int' and 'const unsigned int'

[muiez]

LGTM.

llvm/unittests/Support/Path.cpp

 TEST_F(FileSystemTest, getUmask) {
 #ifdef _WIN32
   EXPECT_EQ(fs::getUmask(), 0U) << "Should always be 0 on Windows.";
 #else
   unsigned OldMask = ::umask(0022);
   unsigned CurrentMask = fs::getUmask();
   EXPECT_EQ(CurrentMask, 0022U)
       << "getUmask() didn't return previously set umask()";
-  EXPECT_EQ(::umask(OldMask), 0022U) << "getUmask() may have changed umask()";
+  EXPECT_EQ(::umask(OldMask), mode_t(0022U))
+      << "getUmask() may have changed umask()";
 #endif
 }
 
 TEST_F(FileSystemTest, RespectUmask) {
 #ifndef _WIN32
   unsigned OldMask = ::umask(0022);
 
   int FD;