Wrap help strings at 80 columns

This patch ensures that all ordinary help strings are wrapped at 80
columns.  For the most part this consists of changing code like this
(note the embedded \n and the trailing backslash without a newline):

-Manage the space-separated list of debuginfod server URLs that GDB will query \
-when missing debuginfo, executables or source files.\nThe default value is \
-copied from the DEBUGINFOD_URLS environment variable."),

... to end each line with \n\, like:

+Manage the space-separated list of debuginfod server URLs that GDB will\n\
+query when missing debuginfo, executables or source files.\n\
+The default value is copied from the DEBUGINFOD_URLS environment variable."),

Approved-By: Eli Zaretskii <eliz@gnu.org>

gdb/frame-unwind.c

@@ -376,7 +376,8 @@ _initialize_frame_unwind ()
   add_cmd ("frame-unwinders",
 	   class_maintenance,
 	   maintenance_info_frame_unwinders,
-	   _("List the frame unwinders currently in effect, "
-	     "starting with the highest priority."),
+	   _("\
+List the frame unwinders currently in effect.\n\
+Unwinders are listed starting with the highest priority."),
 	   &maintenanceinfolist);
 }