msgpack: rename from libmsgpack

The project does not use the name "libmsgpack". It variously uses "msgpack" and
"msgpack-c", and "msgpackc" for the name of the library.

pkgs/development/libraries/msgpack/generic.nix

@@ -0,0 +1,30 @@
+{ stdenv, cmake
+, version, src, patches ? [ ]
+, hostPlatform
+, ...
+}:
+
+stdenv.mkDerivation rec {
+  name = "msgpack-${version}";
+
+  inherit src patches;
+
+  nativeBuildInputs = [ cmake ];
+
+  enableParallelBuilding = true;
+
+  cmakeFlags = []
+    ++ stdenv.lib.optional (stdenv.hostPlatform != stdenv.buildPlatform)
+                           "-DMSGPACK_BUILD_EXAMPLES=OFF"
+    ++ stdenv.lib.optional (hostPlatform.libc == "msvcrt")
+                           "-DCMAKE_SYSTEM_NAME=Windows"
+    ;
+
+  meta = with stdenv.lib; {
+    description = "MessagePack implementation for C and C++";
+    homepage    = https://msgpack.org;
+    license     = licenses.asl20;
+    maintainers = with maintainers; [ redbaron wkennington ];
+    platforms   = platforms.all;
+  };
+}