Support GNU/kFreeBSD

GNU/kFreeBSD = FreeBSD kernel + userspace with glibc.  Linux.cmake
doesn't contain anything too OS specific, so we can forward to it.

Here are outputs of /bin/uname on author's machine:
  uname -p ==> i386
  uname -o ==> GNU/kFreeBSD
  uname -s ==> GNU/kFreeBSD
  uname -r ==> 5.4-1-686

Patch from Modestas Vainius.  See issue #9659.

Modules/CMakeDetermineSystem.cmake

@@ -25,6 +25,7 @@
 # HP-UX                         HP-UX  
 # IRIX                          IRIX  
 # Linux                         Linux  
+# GNU/kFreeBSD                  GNU/kFreeBSD
 # NetBSD                        NetBSD  
 # OpenBSD                       OpenBSD  
 # OFS/1 (Digital Unix)          OSF1  
@@ -121,6 +122,11 @@ MACRO(ADJUST_CMAKE_SYSTEM_VARIABLES _PREFIX)
     SET(${_PREFIX}_NAME BSDOS)
   ENDIF(${_PREFIX}_NAME MATCHES BSD.OS)
 
+  # fix for GNU/kFreeBSD, remove the GNU/
+  IF(${_PREFIX}_NAME MATCHES kFreeBSD)
+    SET(${_PREFIX}_NAME kFreeBSD)
+  ENDIF(${_PREFIX}_NAME MATCHES kFreeBSD)
+
   # fix for CYGWIN which has windows version in it 
   IF(${_PREFIX}_NAME MATCHES CYGWIN)
     SET(${_PREFIX}_NAME CYGWIN)