Fixed a g++ explicit constructor compatibility error for unordered_set. (#935)

* Fixed a g++ explicit constructor compatibility error for unordered_set.

* Change std::unordered_set<std::basic_string<char>>() to
std::unordered_set<std::string>().

include/tvm/build_module.h

@@ -40,7 +40,8 @@ struct Target {
          int thread_warp_size,
          const std::unordered_set<std::string>& keys,
          const std::vector<std::string>& options,
-         const std::unordered_set<std::string>& libs = {}) :
+         const std::unordered_set<std::string>& libs =
+           std::unordered_set<std::string>()) :
     target_name(target_name),
     device_type(device_type),
     max_num_threads(max_num_threads),

src/codegen/build_module.cc

@@ -85,25 +85,29 @@ namespace target {
 Target llvm() {
   std::unordered_set<std::string> keys({ "llvm", "cpu" });
   std::vector<std::string> options;
-  return Target("llvm", kDLCPU, 512, 1, keys, options, {});
+  return Target("llvm", kDLCPU, 512, 1, keys, options,
+           std::unordered_set<std::string>());
 }
 
 Target cuda() {
   std::unordered_set<std::string> keys({ "cuda", "gpu" });
   std::vector<std::string> options;
-  return Target("cuda", kDLGPU, 512, 32, keys, options, {});
+  return Target("cuda", kDLGPU, 512, 32, keys, options,
+           std::unordered_set<std::string>());
 }
 
 Target rocm() {
   std::unordered_set<std::string> keys({ "rocm", "gpu" });
   std::vector<std::string> options;
-  return Target("rocm", kDLROCM, 256, 1, keys, options, {});
+  return Target("rocm", kDLROCM, 256, 1, keys, options,
+           std::unordered_set<std::string>());
 }
 
 Target metal() {
   std::unordered_set<std::string> keys({ "gpu" });
   std::vector<std::string> options;
-  return Target("metal", kDLMetal, 256, 1, keys, options, {});
+  return Target("metal", kDLMetal, 256, 1, keys, options,
+           std::unordered_set<std::string>());
 }
 
 Target rasp() {
@@ -114,7 +118,8 @@ Target rasp() {
     "-mcpu=cortex-a53",
     "-mattr=+neon"
   });
-  return Target("llvm", kDLCPU, 512, 1, keys, options, {});
+  return Target("llvm", kDLCPU, 512, 1, keys, options,
+           std::unordered_set<std::string>());
 }
 
 Target mali() {
@@ -129,7 +134,8 @@ Target mali() {
 Target stackvm() {
   std::unordered_set<std::string> keys({ "stackvm", "cpu" });
   std::vector<std::string> options;
-  return Target("stackvm", kDLCPU, 512, 1, keys, options, {});
+  return Target("stackvm", kDLCPU, 512, 1, keys, options,
+           std::unordered_set<std::string>());
 }
 }  // namespace target