yarp: default to building shared libraries.

Formula/yarp.rb

@@ -6,6 +6,8 @@ class Yarp < Formula
   url "https://github.com/robotology/yarp/archive/v2.3.62.tar.gz"
   sha1 "148fc9d77cc4b68119c31066b452e9607de0f066"
 
+  option "without-shared", "Build only static version of YARP libraries"
+
   depends_on "pkg-config" => :build
   depends_on "cmake" => :build
   depends_on "ace"
@@ -37,7 +39,14 @@ class Yarp < Formula
       -DCREATE_YARPVIEW=TRUE
       -DCREATE_YARPSCOPE=TRUE
       -DCREATE_GYARPMANAGER=TRUE
-      .]
+      ]
+
+      if build.without? "shared"
+        args << "-DCREATE_SHARED_LIBRARY:BOOL=FALSE"
+      else
+        args << "-DCREATE_SHARED_LIBRARY:BOOL=TRUE"
+      end
+      args << "."
 
     system "cmake", *args
     system "make", "install"