lastfmlib: fails with clang

Fixes Homebrew/homebrew#12826.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/lastfmlib.rb

@@ -7,6 +7,15 @@ class Lastfmlib < Formula
 
   depends_on 'pkg-config' => :build
 
+  fails_with :clang do
+    build 318
+    cause <<-EOS.undent
+      lastfmlib/utils/stringoperations.h:62:16: error: no viable conversion from
+            '__string_type' (aka 'basic_string<wchar_t, std::char_traits<wchar_t>,
+            std::allocator<wchar_t> >') to 'std::string' (aka 'basic_string<char>')
+      EOS
+  end
+
   def install
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"