Use version 2.1.0 of libsbsms

This is actually the exact code we already use, but Clayton has
set up a github repo for the release to make it available to
distros.

src/CMakeLists.txt

@@ -1060,7 +1060,7 @@ list( APPEND LIBRARIES
       $<$<BOOL:${USE_MIDI}>:portsmf>
       $<$<BOOL:${USE_NYQUIST}>:libnyquist>
       $<$<BOOL:${USE_PORTMIXER}>:portmixer>
-      $<$<BOOL:${USE_SBSMS}>:sbsms>
+      $<$<BOOL:${USE_SBSMS}>:libsbsms>
       $<$<BOOL:${USE_SOUNDTOUCH}>:soundtouch>
       $<$<BOOL:${USE_VAMP}>:libvamp>
       $<$<PLATFORM_ID:Linux,FreeBSD,OpenBSD,NetBSD,CYGWIN>:PkgConfig::GLIB>