Update cmake modules from Gnuradio to fix parallel build bug

cmake/Modules/GrPlatform.cmake

@@ -1,17 +1,17 @@
 # Copyright 2011 Free Software Foundation, Inc.
-# 
+#
 # This file is part of GNU Radio
-# 
+#
 # GNU Radio is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation; either version 3, or (at your option)
 # any later version.
-# 
+#
 # GNU Radio is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
-# 
+#
 # You should have received a copy of the GNU General Public License
 # along with GNU Radio; see the file COPYING.  If not, write to
 # the Free Software Foundation, Inc., 51 Franklin Street,
@@ -37,10 +37,18 @@ if(LINUX AND EXISTS "/etc/redhat-release")
     set(REDHAT TRUE)
 endif()
 
+if(LINUX AND EXISTS "/etc/slackware-version")
+    set(SLACKWARE TRUE)
+endif()
+
 ########################################################################
 # when the library suffix should be 64 (applies to redhat linux family)
 ########################################################################
-if(NOT DEFINED LIB_SUFFIX AND REDHAT AND CMAKE_SYSTEM_PROCESSOR MATCHES "64$")
+if (REDHAT OR SLACKWARE)
+    set(LIB64_CONVENTION TRUE)
+endif()
+
+if(NOT DEFINED LIB_SUFFIX AND LIB64_CONVENTION AND CMAKE_SYSTEM_PROCESSOR MATCHES "64$")
     set(LIB_SUFFIX 64)
 endif()
 set(LIB_SUFFIX ${LIB_SUFFIX} CACHE STRING "lib directory suffix")