cmake: Add FindTaglib.cmake.

extras/buildsystem/cmake/include/FindTaglib.cmake

+# - Find library containing Taglib()
+# The following variables are set if Taglib is found. If Taglib is not
+# found, Taglib_FOUND is set to false.
+#  Taglib_FOUND     - System has Taglib.
+#  Taglib_LIBRARIES - Link these to use Taglib.
+#  Taglib_CFLAGS - Link these to use Taglib.
+
+
+if (NOT Taglib_SEARCHED)
+    include(CheckLibraryExists)
+
+    set(Taglib_SEARCHED TRUE CACHE INTERNAL "")
+    set(Taglib_FOUND FALSE CACHE INTERNAL "")
+
+    pkg_check_modules(Taglib taglib)
+
+    if (Taglib_FOUND)
+      if (NOT Taglib_FIND_QUIETLY)
+        message(STATUS "Found Taglib in: ${Taglib_LIBRARIES}")
+      endif (NOT Taglib_FIND_QUIETLY)
+    else (Taglib_FOUND)
+      if (Taglib_FIND_REQUIRED)
+        message(FATAL_ERROR "Could not find the library containing Taglib")
+      endif (Taglib_FIND_REQUIRED)
+    endif (Taglib_FOUND)
+
+    mark_as_advanced(Taglib_LIBRARIES)
+endif(NOT Taglib_SEARCHED)