[Ada] Implement pragma Compiler_Unit_Warning

[Arnaud Charlet <charlet at adacore dot com>]

A new pragma Compiler_Unit_Warning replaces the old pragma
Compiler_Unit (which is retained as synonymous so that new
compilers can be used to bootstrap old sources).

The new pragma differs from the old one in two respects

First: the set of things checked for is changed, RAISE WITH
is now allowed, but several new Ada 2012 features are flagged.

Second: the message is a warning, not an error

The reason we made a new pragma here is to deal with bootstrap
issues. We wanted to allow RAISE WITH, and are willing to say
we require GCC 4.1 for bootstrapping. But
just removing the calls to Check_Compiler_Unit for RAISE WITH
wouldn't work. That's because older compilers, even though they
support RAISE WITH fine, don't think this should be allowed in
units with pragma Compiler_Unit.

By changing to a new pragma, older compilers will issue a warning
of unrecognized pragmas in the first build phase, but warnings
are ignored then, and then subsequent phases of the build will
use the latest version of the compiler (and thus the latest set
of choices wrt pragma Compiler_Unit_Warning).

The following test program is compiled with -gnatld7

     1. pragma Compiler_Unit_Warning;
     2.
     3. procedure CUWarn (X : in out Integer) is
     4.    A : Integer;
     5. begin
     6.    if X > 3 then
     7.       A := (if X > 4 then 2 else 1);
                    |
        >>> warning: use of construct not allowed in compiler

     8.    end if;
     9.
    10.    if X in 1 | 2 | 5 then
                |
        >>> warning: use of construct not allowed in compiler

    11.       X := 52;
    12.    end if;
    13.
    14.    raise Constraint_Error with "always raised";
    15. end;

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

2014-02-25  Robert Dewar  <dewar@adacore.com>

	* s-excdeb.ads, s-except.ads, s-exctab.adb, s-exctab.ads, s-finmas.ads,
	s-htable.adb, s-htable.ads, s-imenne.adb, s-imenne.ads, s-imgenu.adb,
	s-imgenu.ads, s-mastop.adb, s-mastop.ads, s-memory-vms_64.adb,
	s-memory-vms_64.ads, s-memory.adb, s-memory.ads, s-os_lib.adb,
	s-os_lib.ads, s-parame.adb, s-parame.ads, s-purexc.ads, s-restri.adb,
	s-restri.ads, s-rident.ads, s-secsta.adb, s-secsta.ads, s-soflin.adb,
	s-soflin.ads, s-sopco3.adb, s-sopco3.ads, s-sopco4.adb, s-sopco4.ads,
	s-sopco5.adb, s-sopco5.ads, s-spsufi.ads, s-stache.adb, s-stache.ads,
	s-stalib.adb, s-stalib.ads, s-stoele.adb, s-stoele.ads, s-strcom.adb,
	s-strcom.ads, s-strhas.adb, s-string.adb, s-string.ads, s-strops.adb,
	s-strops.ads, s-ststop.adb, s-ststop.ads, s-traceb.adb, s-traceb.ads,
	s-traent.adb, s-traent.ads, s-unstyp.ads, s-utf_32.adb, s-utf_32.ads,
	s-wchcnv.adb, s-wchcnv.ads, s-wchcon.adb, s-wchcon.ads, s-wchjis.adb,
	s-wchjis.ads, sem_ch11.adb, sem_ch4.adb, sem_ch5.adb, sem_prag.adb,
	snames.ads-tmpl: Change Compiler_Unit everywhere to
	Compiler_Unit_Warning.

Attachment: difs
Description: Text document