gdbserver: include hostio.h in hostio-errno.c

... so that the definition of hostio_last_error_from_errno in hostio-errno.c
sees the declaration in hostio.h.

Fix this error:

      CXX    hostio-errno.o
    /home/smarchi/src/binutils-gdb/gdb/gdbserver/hostio-errno.c: In function ‘void hostio_last_error_from_errno(char*)’:
    /home/smarchi/src/binutils-gdb/gdb/gdbserver/hostio-errno.c:28:1: error: no previous declaration for ‘void hostio_last_error_from_errno(char*)’ [-Werror=missing-declarations]
     hostio_last_error_from_errno (char *buf)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

gdb/gdbserver/ChangeLog:

	* hostio-errno.c: Include hostio.h.

Change-Id: I056308fd4ce12810d0a1b826c423bd0c7eeb8944

gdb/gdbserver/ChangeLog

@@ -1,3 +1,7 @@
+2020-01-13  Simon Marchi  <simon.marchi@efficios.com>
+
+	* hostio-errno.c: Include hostio.h.
+
 2020-01-13  Simon Marchi  <simon.marchi@efficios.com>
 
 	* Makefile.in (%-generated.c): Make $(regdat_sh) a regular

gdb/gdbserver/hostio-errno.c

@@ -22,6 +22,9 @@
    on top of errno.  */
 
 #include "server.h"
+
+#include "hostio.h"
+
 #include "gdbsupport/fileio.h"
 
 void