[CMAKE] Define _GNU_SOURCE on CMakeLists.txt

The latest elfutils-libelf headers won't compile without _LARGEFILE64_SOURCE
(that is implied by _GNU_SOURCE).

Some .c files don't have a #define _GNU_SOURCE line. Instead of adding the line
to all .c files, define it globally on CMakeLists.txt.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>

CMakeLists.txt

@@ -23,6 +23,7 @@ if (NOT CMAKE_BUILD_TYPE)
 	     FORCE)
 endif (NOT CMAKE_BUILD_TYPE)
 
+add_definitions(-D_GNU_SOURCE)
 find_package(DWARF REQUIRED)
 
 _set_fancy(LIB_INSTALL_DIR "${EXEC_INSTALL_PREFIX}${CMAKE_INSTALL_PREFIX}/${__LIB}" "libdir")

dwarves.c

@@ -9,7 +9,6 @@
   published by the Free Software Foundation.
 */
 
-#define _GNU_SOURCE
 #include <assert.h>
 #include <dirent.h>
 #include <dwarf.h>

pglobal.c

@@ -6,7 +6,6 @@
  * by the Free Software Foundation.
  */
 
-#define _GNU_SOURCE
 #include <argp.h>
 #include <malloc.h>
 #include <search.h>

syscse.c

@@ -8,7 +8,6 @@
   published by the Free Software Foundation.
 */
 
-#define _GNU_SOURCE
 #include <argp.h>
 #include <assert.h>
 #include <stdio.h>