[Ada] Fix parsing for expressions with attributes and characters

Before this change, trying to evaluate the following Ada expression
yielded a syntax error, even though it's completely legal:

    (gdb) p s'first = 'a'
    Error in expression, near `'.

The problem lies in the lexer (gdb/ada-lex.l): at the point we reach "'a'",
we're still in the BEFORE_QUAL_QUOTE start condition (the mechanism to
distinguish character literals from other "tick" usages: qualified
expressions and attributes), so we consider that this quote is actually a
separate "tick".

This changes resets the start condition to INITIAL in the
{TICK}[a-zA-Z][a-zA-Z]+ rule (for attributes): attributes activate this
BEFORE_QUAL_QUOTE condition and in this case the above rule is always
executed rather than the <BEFORE_QUAL_QUOTE>"'" one (in flex, it's
always the longest match that is chosen). We now have instead:

    (gdb) p s'first = 'a'
    $1 = true

gdb/ChangeLog:

	* ada-lex.l: Reset the start condition to INITIAL in the rule
	that matches attributes.

gdb/testsuite/ChangeLog:

	* gdb.ada/attr_ref_and_charlit.exp: New testcase.
	* gdb.ada/attr_ref_and_charlit/foo.adb: New file.

Tested on x86_64-linux, no regression.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2015-08-20  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* ada-lex.l: Reset the start condition to INITIAL in the rule that
+	matches attributes.
+
 2015-08-19  Kevin Buettner  <kevinb@redhat.com>
 
 	* dwarf2read.c (dwarf2_string_attr): New function.

gdb/ada-lex.l

@@ -205,7 +205,7 @@ false		{ return FALSEKEYWORD; }
 
         /* ATTRIBUTES */
 
-{TICK}[a-zA-Z][a-zA-Z]+ { return processAttribute (yytext+1); }
+{TICK}[a-zA-Z][a-zA-Z]+ { BEGIN INITIAL; return processAttribute (yytext+1); }
 
 	/* PUNCTUATION */
 

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2015-08-20  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* gdb.ada/attr_ref_and_charlit.exp: New testcase.
+	* gdb.ada/attr_ref_and_charlit/foo.adb: New file.
+
 2015-08-19  Kevin Buettner  <kevinb@redhat.com>
     
 	* gdb.dwarf2/dw2-bad-mips-linkage-name.c: New file.

gdb/testsuite/gdb.ada/attr_ref_and_charlit.exp

@@ -0,0 +1,42 @@
+# Copyright 2015 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib "ada.exp"
+
+standard_ada_testfile "foo"
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+set bp_location [gdb_get_line_number "BREAK" "${testdir}/foo.adb"]
+
+# Check with the same array at two different points in the execution that using
+# both an attribute reference and a character literal in the same expression
+# work as expected. They used to yield syntax error.
+
+runto "foo.adb:$bp_location"
+gdb_test "print s'first" " = 2"
+gdb_test "print s'last"  " = 3"
+gdb_test "print s(s'first) = 'a'" " = true"
+gdb_test "print s(s'last) /= 'b'" " = false"
+
+gdb_test "continue" \
+         ".*Breakpoint \[0-9\]+, foo\\.p \\(s=.*\\) at .*foo.adb:\[0-9\]+.*" \
+gdb_test "print s'first" " = 4"
+gdb_test "print s'last"  " = 5"
+gdb_test "print s(s'first) = 'c'" " = true"
+gdb_test "print s(s'last) /= 'd'" " = false"

gdb/testsuite/gdb.ada/attr_ref_and_charlit/foo.adb

@@ -0,0 +1,24 @@
+--  Copyright 2015 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+procedure Foo is
+   procedure P (S : String) is
+   begin
+      null; -- BREAK
+   end P;
+begin
+   P ((2 => 'a', 3 => 'b'));
+   P ((4 => 'c', 5 => 'd'));
+end Foo;