[Ada] Check component overlap when non-standard bit-order

[Arnaud Charlet <charlet at adacore dot com>]

Previously, the check for record component overlap was done at the time
of analyzing the record representation clause. But that's too early since
non-standard bit order affects the results. This patch defers overlap
checking till freeze time. The following test program shows an overlap
which was not previously detected:

     1. pragma Ada_05;
     2. with System; use System;
     3. package NS_Bit_Order_Overlap is
     4.   type Rec is record
     5.     I1, I2, I3, I4: Integer range 0 .. 2**15 - 1;
     6.   end record;
     7.
     8.   for Rec use record         --  LOF       HOF   ~   LOF
     9.     I1 at 0 range  0 .. 15;  -- 0 0 15    6 0 15 ~ 48 .. 63
                           |
        >>> info: reverse bit order in machine scalar of length 64
        >>> info: little-endian range for component "I1" is 48 .. 63

    10.     I2 at 0 range 16 .. 31;  -- 2 0 15    4 0 15 ~ 32 .. 47
                          |
        >>> info: reverse bit order in machine scalar of length 64
        >>> info: little-endian range for component "I2" is 32 .. 47

    11.     I3 at 0 range 32 .. 47;  -- 4 0 15    2 0 15 ~ 16 .. 31
                          |
        >>> info: reverse bit order in machine scalar of length 64
        >>> info: little-endian range for component "I3" is 16 .. 31

    12.     I4 at 4 range 16 .. 31;  -- 6 0 15    4 0 15 ~  0 .. 15
            1             2
        >>> component "I4" overlaps "I2" at line 10
        >>> info: reverse bit order in machine scalar of length 32
        >>> info: little-endian range for component "I4" is 0 .. 15

    13.   end record;
    14.    for Rec'Bit_Order use
    15.      Bit_Order'Val (1 - Bit_Order'Pos (Default_Bit_Order));
    16. end;

Tested on x86_64-pc-linux-gnu, committed on trunk

2010-06-17  Robert Dewar  <dewar@adacore.com>

	* einfo.ads, einfo.adb (Get_Record_Representation_Clause): New function.
	* freeze.adb (Freeze_Record_Type): Add call to
	Check_Record_Representation_Clause.
	* sem_ch13.adb (Check_Record_Representation_Clause): New function
	(Analyze_Record_Representation_Clause): Split out overlap code into this
	new function.
	(Check_Component_Overlap): Moved inside
	Check_Record_Representation_Clause.
	* sem_ch13.ads (Check_Record_Representation_Clause): New function.

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