Debug mode for string. This commit also marks the first time libc++ debug-mode has found a bug (found one in regex). Had to play with extern templates a bit to get this to work since string is heavily used within libc++.dylib.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@189114 91177308-0d34-0410-b5e6-96231b3b80d8

test/strings/basic.string/string.modifiers/string_insert/iter_iter_iter.pass.cpp

@@ -12,6 +12,10 @@
 // template<class InputIterator>
 //   iterator insert(const_iterator p, InputIterator first, InputIterator last);
 
+#if _LIBCPP_DEBUG2 >= 1
+#define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
+#endif
+
 #include <string>
 #include <cassert>
 
@@ -123,4 +127,14 @@ int main()
          S("12345678901234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"));
     }
 #endif
+#if _LIBCPP_DEBUG2 >= 1
+    {
+        std::string v;
+        std::string v2;
+        char a[] = "123";
+        const int N = sizeof(a)/sizeof(a[0]);
+        std::string::iterator i = v.insert(v2.cbegin() + 10, a, a+N);
+        assert(false);
+    }
+#endif
 }