CMakeLists.txt: use pkg-config to detect uuid when possible

In order to take into account the libraries used by libuuid when
building statically, using pkg-config is recommended. This patch
therefore improves the CMakeLists.txt to use pkg-config to detect
libuuid when pkg-config is available.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/CMakeLists.txt
===================================================================
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,6 +6,7 @@
 
 include (CheckFunctionExists)
 include (CheckStructHasMember)
+include (FindPkgConfig)
 
 set (HAVE_CMAKE true)
 
@@ -119,8 +120,16 @@
   # Apple and FreeBSD include the uuid functions in their libc, rather than libuuid
   check_function_exists (uuid_unparse_lower HAVE_UUID_UNPARSE_LOWER)
 else (DARWIN OR FREEBSD)
-  find_path    (UUID_INCLUDE_DIR   uuid/uuid.h)
-  find_library (UUID_LIBRARY NAMES uuid)
+  if(PKG_CONFIG_FOUND)
+    pkg_check_modules(PC_UUID uuid)
+    if(PC_UUID_FOUND)
+      set (UUID_INCLUDE_DIR ${PC_UUID_INCLUDE_DIRS})
+      set (UUID_LIBRARY ${PC_UUID_LIBRARIES})
+    endif(PC_UUID_FOUND)
+  else(PKG_CONFIG_FOUND)
+    find_path    (UUID_INCLUDE_DIR   uuid/uuid.h)
+    find_library (UUID_LIBRARY NAMES uuid)
+  endif(PKG_CONFIG_FOUND)
   if (UUID_INCLUDE_DIR AND UUID_LIBRARY)
     set (TASKD_INCLUDE_DIRS ${TASKD_INCLUDE_DIRS} ${UUID_INCLUDE_DIR})
     set (TASKD_LIBRARIES    ${TASKD_LIBRARIES}    ${UUID_LIBRARY})