Wrap recv to avoid warnings

Avoid warnings like these by wrapping recv():
  CC    slirp/ip_icmp.o
/src/qemu/slirp/ip_icmp.c: In function 'icmp_receive':
/src/qemu/slirp/ip_icmp.c:418:5: error: passing argument 2 of 'recv' from incompatible pointer type [-Werror]
/usr/local/lib/gcc/i686-mingw32msvc/4.6.0/../../../../i686-mingw32msvc/include/winsock2.h:547:32: note: expected 'char *' but argument is of type 'struct icmp *'

Remove also casts used to avoid warnings.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/qemu-common.h b/qemu-common.h
index ba55719..391fadd 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -200,6 +200,12 @@
 int qemu_pipe(int pipefd[2]);
 #endif
 
+#ifdef _WIN32
+#define qemu_recv(sockfd, buf, len, flags) recv(sockfd, (void *)buf, len, flags)
+#else
+#define qemu_recv(sockfd, buf, len, flags) recv(sockfd, buf, len, flags)
+#endif
+
 /* Error handling.  */
 
 void QEMU_NORETURN hw_error(const char *fmt, ...) GCC_FMT_ATTR(1, 2);