JIT patch: add gcc_jit_magic_int

[Basile Starynkevitch]

Hello All,

As I explained in https://gcc.gnu.org/ml/jit/2016-q2/msg00042.html it is 
difficult (or tricky without using dirty tricks involving the GCC plugin 
headers) to use GCCJIT to emit code equivalent to the following C file:

    extern int a;
    int get_atomic_a (void) {
      return __atomic_load_n (&a, __ATOMIC_SEQ_CST);
    }

The issue is that __ATOMIC_SEQ_CST is a magic preprocessor (but non-standard!) symbol which might not be available
(or might have a different value) in the C code for GCCJIT building such an AST.

So we need a function to retrieve some magic integral value from the GCCJIT compiler.

The attached patch (relative to trunk svn 236583) is a first attempt to solve that issue
  (and also give ability to query some other magic numbers).

Proposed ChangeLog entry (in gcc/jit/)

2016-05-23  Basile Starynkevitch  <basile@starynkevitch.net>
	* libgccjit.h (LIBGCCJIT_HAVE_gcc_jit_magic_int): New macro.
	(gcc_jit_magic_int): New public function declaration.

	* libgccjit.c: Include "cppbuiltin.h", "options.h", "flag-types.h"
	(gcc_jit_magic_int): New function.

	* libgccjit.map: Add gcc_jit_magic_int to LIBGCCJIT_ABI_6.

Comments (or an ok to commit) are welcome. (I am not sure that __SANITIZE_ADDRESS__ is correctly handled,
because I would believe that optimization flags are not globals in GCCJIT)

Regards.

-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mine, sont seulement les miennes} ***

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