Fix a Sparse warning about redefinition of offsetof()

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

configure

@@ -1602,6 +1602,18 @@ if test "$darwin" != "yes" -a "$mingw32" != "yes" -a "$solaries" != yes -a \
     libs_softmmu="-lutil $libs_softmmu"
 fi
 
+##########################################
+# check if the compiler defines offsetof
+
+need_offsetof=yes
+cat > $TMPC << EOF
+#include <stddef.h>
+int main(void) { struct s { int f; }; return offsetof(struct s, f); }
+EOF
+if compile_prog "" "" ; then
+    need_offsetof=no
+fi
+
 # End of CC checks
 # After here, no more $cc or $ld runs
 
@@ -1901,6 +1913,9 @@ fi
 if test "$fdt" = "yes" ; then
   echo "CONFIG_FDT=y" >> $config_host_mak
 fi
+if test "$need_offsetof" = "yes" ; then
+  echo "CONFIG_NEED_OFFSETOF=y" >> $config_host_mak
+fi
 
 # XXX: suppress that
 if [ "$bsd" = "yes" ] ; then

osdep.h

@@ -2,6 +2,7 @@
 #define QEMU_OSDEP_H
 
 #include <stdarg.h>
+#include <stddef.h>
 #ifdef __OpenBSD__
 #include <sys/types.h>
 #include <sys/signal.h>
@@ -27,7 +28,7 @@
 #define unlikely(x)   __builtin_expect(!!(x), 0)
 #endif
 
-#ifndef offsetof
+#ifdef CONFIG_NEED_OFFSETOF
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *) 0)->MEMBER)
 #endif
 #ifndef container_of