[NFC] Properly handle optional minor value for ArchInfo::Version

Use `value_or` instead of `value` for checking minor versions in
`ArchInfo::implies`.

Differential Revision: https://reviews.llvm.org/D145206

Author: zixu-w

llvm/include/llvm/TargetParser/AArch64TargetParser.h

@@ -288,8 +288,8 @@ struct ArchInfo {
       return this->Version > Other.Version;
     }
     if (this->Version.getMajor() == 9 && Other.Version.getMajor() == 8) {
-      return this->Version.getMinor().value() + 5 >=
-             Other.Version.getMinor().value();
+      return this->Version.getMinor().value_or(0) + 5 >=
+             Other.Version.getMinor().value_or(0);
     }
     return false;
   }