Set language for Ada minimal symbols.

This helps with the following issue: Given an Ada program defining
a global variable:

    package Pck is
       Watch : Integer := 1974;
    end Pck;

When printing the address of this variable, GDB also tries to print
the associated symbol name:

    (gdb) p watch'address
    $1 = (access integer) 0x6139d8 <pck__watch>
                                       ^^
                                       ||

The problem is that GDB prints the variable's linkage name, instead
of its natural name. This is because the language of the associated
minimal symbol never really gets set.

This patch adds handling for Ada symbols in symbol_find_demangled_name.
After this patch, we now get:

    (gdb) p watch'address
    $1 = (access integer) 0x6139d8 <pck.watch>
                                       ^
                                       |

gdb/ChangeLog:

        * symtab.c (symbol_find_demangled_name): Add handling of
        Ada symbols.

gdb/testsuite/ChangeLog:

        * gdb.ada/int_deref.exp: Add test verifying that we print
        the decoded symbol name when printing the address of Ada
        symbols.

gdb/testsuite/gdb.ada/int_deref.exp

@@ -26,6 +26,11 @@ clean_restart ${testfile}
 set bp_location [gdb_get_line_number "Pck.Watch" ${testdir}/foo.adb]
 runto "foo.adb:$bp_location"
 
+# Hijack a bit this testcase, to verify that name decoding works
+# when doing symbolic address printing.
+gdb_test "print watch'address" \
+         " = \\(system\\.address\\) $hex <pck\\.watch>"
+
 gdb_test "print *long_integer(watch'address)" \
          " = 4874"