Fix libsnark dependency build.

This changes libsnark to build in-place, instead of copying first to
a build directory. Previously, modifications made to the original
sources wouldn't get rebuilt without a 'make clean' because users
would be pointing to the copies.

This closes #2689.

src/snark/libsnark/common/utils.tcc

@@ -0,0 +1,23 @@
+/** @file
+ *****************************************************************************
+ Implementation of templatized utility functions
+ *****************************************************************************
+ * @author     This file is part of libsnark, developed by SCIPR Lab
+ *             and contributors (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#ifndef UTILS_TCC_
+#define UTILS_TCC_
+
+namespace libsnark {
+
+template<typename T>
+size_t size_in_bits(const std::vector<T> &v)
+{
+    return v.size() * T::size_in_bits();
+}
+
+} // libsnark
+
+#endif // UTILS_TCC_