Fix build with Clang6

/usr/include/c++/v1/utility:639:1: note: candidate function not viable: 1st
      argument ('const std::string' (aka 'const basic_string<char,
      char_traits<char>, allocator<char> >')) would lose const qualifier
make_pair(_T1&& __t1, _T2&& __t2)

Patch includes more explanation.

Reported by:	linimon

1 files changed, 16 insertions, 0 deletions

diff --git a/games/supertux/files/patch-src_music__manager.cpp b/games/supertux/files/patch-src_music__manager.cpp
new file mode 100644
index 000000000000..f9a312c15f28
--- /dev/null
+++ b/games/supertux/files/patch-src_music__manager.cpp
@@ -0,0 +1,16 @@
+Fix build with Clang6.
+
+file is a const std::string&, which needs to be (explicitly) copied
+into the pair when the pair's first member is std::string (non-const).
+
+--- src/music_manager.cpp.orig	2018-07-05 12:45:32 UTC
++++ src/music_manager.cpp
+@@ -66,7 +66,7 @@ MusicManager::exists_music(const std::string& file)
+   // insert into music list
+   std::pair<std::map<std::string, MusicResource>::iterator, bool> result = 
+     musics.insert(
+-        std::make_pair<std::string, MusicResource> (file, MusicResource()));
++        std::make_pair<std::string, MusicResource> (std::string(file), MusicResource()));
+   MusicResource& resource = result.first->second;
+   resource.manager = this;
+   resource.music = song;