[mlir][cmake] Comment out redundant static assert regarding VarInfo struct

[amirBish]

@aartbik as a result of this issue https://github.com/llvm/llvm-project/issues/63773 , I've uploaded this revision which comments out the static_assert() as you've suggested

[aartbik]

mlir/lib/Dialect/SparseTensor/IR/Detail/Var.h

389–390

can you add a TODO indicator, so we remember to bring it back

[amirBish]

TODO indicator for the comment

[mehdi_amini]

I'll land this, gcc-7 build is broken without this.

mlir/lib/Dialect/SparseTensor/IR/Detail/Var.h

constexpr Var getVar() const {
     return Var(kind, *num);
   }
   constexpr std::optional<Var> tryGetVar() const {
     return num ? std::make_optional(Var(kind, *num)) : std::nullopt;
   }
 };
 // We don't actually require this, since `VarInfo` is a proper struct
 // rather than a newtype.  But it passes, so for now we'll keep it around.
-static_assert(IsZeroCostAbstraction<VarInfo>);
+// TODO: Uncomment the static assert, it fails the build with gcc7 right now.
+// static_assert(IsZeroCostAbstraction<VarInfo>);
 
 //===----------------------------------------------------------------------===//
 enum class CreationPolicy { MustNot, May, Must };
 
 class VarEnv final {
   /// Map from `VarKind` to the next free `Var::Num`; used by `bindVar`.
   VarKindArray<Var::Num> nextNum;
   /// Map from `VarInfo::ID` to shared storage for the actual `VarInfo` objects.