gdb: Silence -Wformat-nonliteral warning with clang

We get this warning when building with clang:

      CXX    ui-out.o
    /home/smarchi/src/binutils-gdb/gdb/ui-out.c:590:22: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
      do_message (style, format, args);
                         ^~~~~~

This can be considered a legitimate warning, as call_do_message's format
parameter is not marked as a format string.  Therefore, we should
normally mark the call_do_message method with the `format` attribute.
However, doing so just moves (and multiplies) the problem, as all the
uses of call_do_message in the vmessage method now warn.  If we wanted
to continue on that path, we should silence the warning for each of
them, as a way of telling the compiler "it's ok, we know what we are
doing".

But since call_do_message is really just vmessage's little helper, it's
simpler to just silence the warning at that single point.

gdb/ChangeLog:

	* ui-out.c (ui_out::call_do_message): Silence
	-Wformat-nonliteral warning.

Change-Id: I58ad41793448f38835c5d6ba7b9e5c4dd8df260f

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2019-10-13  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* ui-out.c (ui_out::call_do_message): Silence
+	-Wformat-nonliteral warning.
+
 2019-10-12  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* breakpoint.c: Remove some includes: continuations.h, skip.h,

gdb/ui-out.c

@@ -26,6 +26,7 @@
 #include "ui-out.h"
 #include "gdbsupport/format.h"
 #include "cli/cli-style.h"
+#include "diagnostics.h"
 
 #include <vector>
 #include <memory>
@@ -587,7 +588,15 @@ ui_out::call_do_message (const ui_file_style &style, const char *format,
   va_list args;
 
   va_start (args, format);
+
+  /* Since call_do_message is only used as a helper of vmessage, silence the
+     warning here once instead of at all call sites in vmessage, if we were
+     to put a "format" attribute on call_do_message.  */
+  DIAGNOSTIC_PUSH
+  DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
   do_message (style, format, args);
+  DIAGNOSTIC_POP
+
   va_end (args);
 }