Merge #19: Don't write debug output "Cannot compile arg=%i as {B,W}" to stderr

1bfd709 Don't write debug output "Cannot compile arg=%i as B" to stderr (practicalswift)

Pull request description:

  Don't write debug output `Cannot compile arg=%i as B` to `stderr`.

  Before:

  ```
  $ ./miniscript <<< "thresh(2,sha256(H),sha256(H),or(sha256(H),sha256(H)))"
  Cannot compile arg=2 as B
  Failed to parse as policy or miniscript 'thresh(2,sha256(H),sha256(H),or(sha256(H),sha256(H)))'
  ```

  After:

  ```
  $ ./miniscript <<< "thresh(2,sha256(H),sha256(H),or(sha256(H),sha256(H)))"
  Failed to parse as policy or miniscript 'thresh(2,sha256(H),sha256(H),or(sha256(H),sha256(H)))'
  ```

  Closes #9.

ACKs for commit 1bfd70:
  sipa:
    ACK 1bfd709

Tree-SHA512: ff31fab76c2e31164900d76755f8c28feccef5e9e56461960b9e98c3bd513129fa8bed787f80cf22f74b7f3bcec3f2fc371c09ddb4d8ab524781bd64050525c1

Author: sipa

compiler.cpp

@@ -806,11 +806,11 @@ void Compile(const Strat* strat, Compilation& compilation, std::map<CompilationK
             for (size_t i = 0; i < strat->sub.size(); ++i) {
                 const Compilation& comp = GetCompilation(strat->sub[i], pqs.first[i], pqs.second[i], cache);
                 auto res_B = comp.Query("Bemdu"_mstf);
-                if (res_B.size() == 0) {fprintf(stderr, "Cannot compile arg=%i as B\n", (int)i); return; }
+                if (res_B.size() == 0) { return; }
                 assert(res_B.size() == 1);
                 Bs.push_back(std::move(res_B[0]));
                 auto res_W = comp.Query("Wemdu"_mstf);
-                if (res_W.size() == 0) {fprintf(stderr, "Cannot compile arg=%i as W\n", (int)i); return; }
+                if (res_W.size() == 0) { return; }
                 assert(res_W.size() == 1);
                 Ws.push_back(std::move(res_W[0]));
                 if (Ws.back().cost - Bs.back().cost > cost_diff) {