Allow - in %p for printf

PR cli/19918 points out that a printf format like "%-5p" will cause a
gdb crash.  The bug is problem is that printf_pointer doesn't take the
"-" flag into account.

gdb/ChangeLog
2018-03-14  Tom Tromey  <tom@tromey.com>

	PR cli/19918:
	* printcmd.c (printf_pointer): Allow "-" in format.

gdb/testsuite/ChangeLog
2018-03-14  Tom Tromey  <tom@tromey.com>

	PR cli/19918:
	* gdb.base/printcmds.exp (test_printf): Add printf test using '-'
	flag.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2018-03-14  Tom Tromey  <tom@tromey.com>
+
+	PR cli/19918:
+	* printcmd.c (printf_pointer): Allow "-" in format.
+
 2018-03-14  Tom Tromey  <tom@tromey.com>
 
 	* printcmd.c (_initialize_printcmd): Add usage to printf.

gdb/printcmd.c

@@ -2399,8 +2399,9 @@ printf_pointer (struct ui_file *stream, const char *format,
   if (val != 0)
     *fmt_p++ = '#';
 
-  /* Copy any width.  */
-  while (*p >= '0' && *p < '9')
+  /* Copy any width or flags.  Only the "-" flag is valid for pointers
+     -- see the format_pieces constructor.  */
+  while (*p == '-' || (*p >= '0' && *p < '9'))
     *fmt_p++ = *p++;
 
   gdb_assert (*p == 'p' && *(p + 1) == '\0');

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2018-03-14  Tom Tromey  <tom@tromey.com>
+
+	PR cli/19918:
+	* gdb.base/printcmds.exp (test_printf): Add printf test using '-'
+	flag.
+
 2018-03-08  Simon Marchi  <simon.marchi@ericsson.com>
 
 	PR gdb/22841

gdb/testsuite/gdb.base/printcmds.exp

@@ -776,6 +776,10 @@ proc test_printf {} {
 	"" \
 	"create hibob command"
     gdb_test "hibob" "hi bob zzz.*y" "run hibob command"
+
+    # PR cli/19918.
+    gdb_test "printf \"%-16dq\\n\", 0" "0               q"
+    gdb_test "printf \"%-16pq\\n\", 0" "\\(nil\\)           q"
 }
 
 #Test printing DFP values with printf