[gdb] Fix clang buildbreaker

Building gdb with clang, I run into:
...
src/gdb/gdbserver/linux-low.c:6190:41: error: comparison of unsigned \
  expression < 0 is always false [-Werror,-Wtautological-compare]
          if (debug_write ("sigchld_handler\n",
                           sizeof ("sigchld_handler\n") - 1) < 0)
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~
...

This regression is introduced by commit a7e559cc08 "gdbserver: Ensure all
debug output uses debug functions", which replaces calls to write with result
type ssize_t with calls to debug_write with result type size_t.

Fix this by making debug_write return ssize_t.

Build and reg-tested on x86_64-linux.

gdb/gdbserver/ChangeLog:

2019-06-19  Tom de Vries  <tdevries@suse.de>

	* debug.h (debug_write): Change return type to ssize_t.
	* debug.c (debug_write): Same.

1 files changed, 1 insertions, 1 deletions

diff --git a/gdb/gdbserver/debug.c b/gdb/gdbserver/debug.c
index a1cf5db..19f11fc 100644
--- a/gdb/gdbserver/debug.c
+++ b/gdb/gdbserver/debug.c
@@ -133,7 +133,7 @@ do_debug_exit (const char *function_name)
 
 /* See debug.h.  */
 
-size_t
+ssize_t
 debug_write (const void *buf, size_t nbyte)
 {
   int fd = fileno (debug_file);