[NFC][AsmPrinter] Windows warning: Use explicit cast

[dstuttard]

Summary

static_cast for uint64_t to unsigned gives a MS VC build warning
for Windows:

warning C4309: 'static_cast': truncation of constant value

Use an explicit cast instead.

Change-Id: I692d335b4913070686a102780c1fb05b893a2f69

[dstuttard]

More in line with other similar fixes

[HsiangKai]

LGTM.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

static void emitComments(const MachineInstr &MI, raw_ostream &CommentOS) {
 
   // We assume a single instruction only has a spill or reload, not
   // both.
   Optional<unsigned> Size;
   if ((Size = MI.getRestoreSize(TII))) {
     CommentOS << *Size << "-byte Reload\n";
   } else if ((Size = MI.getFoldedRestoreSize(TII))) {
     if (*Size) {
-      if (*Size == static_cast<unsigned>(MemoryLocation::UnknownSize))
+      if (*Size == (unsigned)MemoryLocation::UnknownSize)
         CommentOS << "Unknown-size Folded Reload\n";
       else
         CommentOS << *Size << "-byte Folded Reload\n";
     }
   } else if ((Size = MI.getSpillSize(TII))) {
     CommentOS << *Size << "-byte Spill\n";
   } else if ((Size = MI.getFoldedSpillSize(TII))) {
     if (*Size) {
-      if (*Size == static_cast<unsigned>(MemoryLocation::UnknownSize))
+      if (*Size == (unsigned)MemoryLocation::UnknownSize)
         CommentOS << "Unknown-size Folded Spill\n";
       else
         CommentOS << *Size << "-byte Folded Spill\n";
     }
   }
 
   // Check for spill-induced copies
   if (MI.getAsmPrinterFlag(MachineInstr::ReloadReuse))