[NFC] Make the type of X86AlignBranchBoundary compatible

Change the type of X86AlignBranchBoundary from cl::opt<uint64_t> to
cl::opt<unsigned> since the template class cl::opt is only instantiated with
type unsigned, int, std::string, char and bool.

Author: KanRobert

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -117,7 +117,7 @@ class X86AlignBranchKind {
 
 X86AlignBranchKind X86AlignBranchKindLoc;
 
-cl::opt<uint64_t> X86AlignBranchBoundary(
+cl::opt<unsigned> X86AlignBranchBoundary(
     "x86-align-branch-boundary", cl::init(0),
     cl::desc(
         "Control how the assembler should align branches with NOP. If the "