Use what seems to be an unoptimized version for better cross compiling compatibility.

Fixes windows build (other oses need to be tested).

src/snark/src/algebra/fields/bigint.tcc

@@ -104,7 +104,7 @@ bool bigint<n>::is_zero() const
 template<mp_size_t n>
 size_t bigint<n>::num_bits() const
 {
-/*
+
     for (long long i = max_bits(); i >= 0; --i)
     {
         if (this->test_bit(i))
@@ -114,7 +114,7 @@ size_t bigint<n>::num_bits() const
     }
 
     return 0;
-*/
+/*
     for (long long i = n-1; i >= 0; --i)
     {
         mp_limb_t x = this->data[i];
@@ -128,6 +128,7 @@ size_t bigint<n>::num_bits() const
         }
     }
     return 0;
+*/
 }
 
 template<mp_size_t n>