Revert "build: Solve mingw build clash with DATADIR"

This reverts commit 8a8e8656.

The patch was premature, as it still fails to build on mingw at least
in the environment used by
https://travis-ci.org/libvirt/libvirt/jobs/569132417Signed-off-by: NEric Blake <eblake@redhat.com>

src/conf/checkpoint_conf.c

@@ -21,6 +21,8 @@
 
 #include <config.h>
 
+#include <unistd.h>
+
 #include "configmake.h"
 #include "internal.h"
 #include "virbitmap.h"

src/util/viratomic.h

@@ -218,10 +218,7 @@ VIR_STATIC unsigned int virAtomicIntXor(volatile unsigned int *atomic,
 
 # ifdef VIR_ATOMIC_OPS_WIN32
 
-#  pragma push_macro("DATADIR") /* If "configmake.h" was included first */
-#  undef DATADIR
 #  include <winsock2.h>
-#  pragma pop_macro("DATADIR")
 #  include <windows.h>
 #  include <intrin.h>
 #  if !defined(_M_AMD64) && !defined (_M_IA64) && !defined(_M_X64)