Warn if missing debug info for Ada exception catchpoints

This patch should help the user understand why the debugger is not
able to insert Ada exception catchpoints when the Ada runtime was
stripped of debugging info, as is often the case on many GNU/Linux
distros:

    (gdb) catch exception
    Your Ada runtime appears to be missing some debugging information.
    Cannot insert Ada exception catchpoint in this configuration.

gdb/ChangeLog:

        * ada-lang.c (ada_has_this_exception_support): Raise an error
        if we could find the Ada exception hook in the Ada runtime,
        but no debugging info for that hook.

gdb/testsuite/ChangeLog:

        * gdb.ada/catch_ex.exp, gdb.ada/mi_catch_ex.exp: Adjust
        expected output for unsupported case.

1 files changed, 22 insertions, 1 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 66d7420..1a3a975 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -10659,7 +10659,28 @@ ada_has_this_exception_support (const struct exception_support_info *einfo)
 
   sym = standard_lookup (einfo->catch_exception_sym, NULL, VAR_DOMAIN);
   if (sym == NULL)
-    return 0;
+    {
+      /* Perhaps we did not find our symbol because the Ada runtime was
+	 compiled without debugging info, or simply stripped of it.
+	 It happens on some GNU/Linux distributions for instance, where
+	 users have to install a separate debug package in order to get
+	 the runtime's debugging info.  In that situation, let the user
+	 know why we cannot insert an Ada exception catchpoint.
+
+	 Note: Just for the purpose of inserting our Ada exception
+	 catchpoint, we could rely purely on the associated minimal symbol.
+	 But we would be operating in degraded mode anyway, since we are
+	 still lacking the debugging info needed later on to extract
+	 the name of the exception being raised (this name is printed in
+	 the catchpoint message, and is also used when trying to catch
+	 a specific exception).  We do not handle this case for now.  */
+      if (lookup_minimal_symbol (einfo->catch_exception_sym, NULL, NULL))
+	error (_("Your Ada runtime appears to be missing some debugging "
+		 "information.\nCannot insert Ada exception catchpoint "
+		 "in this configuration."));
+
+      return 0;
+    }
 
   /* Make sure that the symbol we found corresponds to a function.  */