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/gadgetlib1/constraint_profiling.cpp

@@ -0,0 +1,48 @@
+/** @file
+ *****************************************************************************
+
+ Implementation of interfaces for profiling constraints.
+
+ See constraint_profiling.hpp .
+
+ *****************************************************************************
+ * @author     This file is part of libsnark, developed by SCIPR Lab
+ *             and contributors (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#include "gadgetlib1/constraint_profiling.hpp"
+#include "common/profiling.hpp"
+
+namespace libsnark {
+
+size_t constraint_profiling_indent = 0;
+std::vector<constraint_profiling_entry> constraint_profiling_table;
+
+size_t PRINT_CONSTRAINT_PROFILING()
+{
+    size_t accounted = 0;
+    print_indent();
+    printf("Constraint profiling:\n");
+    for (constraint_profiling_entry &ent : constraint_profiling_table)
+    {
+        if (ent.indent == 0)
+        {
+            accounted += ent.count;
+        }
+
+        print_indent();
+        for (size_t i = 0; i < ent.indent; ++i)
+        {
+            printf("  ");
+        }
+        printf("* Number of constraints in [%s]: %zu\n", ent.annotation.c_str(), ent.count);
+    }
+
+    constraint_profiling_table.clear();
+    constraint_profiling_indent = 0;
+
+    return accounted;
+}
+
+}