Attach _Alignas to names and refactor _Alignas checks (#133)

* Refactor common code of alignas.

Instead of working on attributes the function now works directly
on the type since the check always performed an extraction of
attributes from a type. 
Bug 23393

* Attach _Alignas to the name.

Bug 23393

* Attach "aligned" attributes to names

So that __attribute((aligned(N))) remains consistent with _Alignas(N).
gcc and clang apply "aligned" attributes to names, with a special case
for typedefs:
    typedef __attribute((aligned(16))) int int_al_16;
    int_al_16 * p;
    __attribute((aligned(16))) int * q;

For gcc, p is naturally-aligned pointer to 16-aligned int and
q is 16-aligned pointer to naturally-aligned int.

For CompCert with this commit, both p and q are 16-aligned pointers
to naturally-aligned int.

* Resurrect the alignment test involving typedef

The test was removed because it involved an _Alignas in a typedef,
which is no longer supported.  However the same effect can be achieved
with an "aligned" attribute, which is still supported in typedef.

1 files changed, 3 insertions, 6 deletions

diff --git a/test/regression/alignas.c b/test/regression/alignas.c
index 23966b59..777c13a5 100644
--- a/test/regression/alignas.c
+++ b/test/regression/alignas.c
@@ -7,7 +7,7 @@
 #endif
 
 #if  __STDC_VERSION__ < 201100 && defined(__GNUC__)
-#define _Alignas(x) __attribute__((aligned(x)))
+#define _Alignas(x) __attribute((aligned(x)))
 #endif
 
 /* Base type */
@@ -20,10 +20,9 @@ _Alignas(16) int b[3];
 typedef int int3[3];
 _Alignas(16) int3 bb;
 
-#if 0
-typedef _Alignas(16) int int16;
+/* _Alignas is not allowed in typedefs but the "aligned" attribute is */
+typedef __attribute((aligned(16))) int int16;
 int16 bbb[3];
-#endif
 
 char filler2;
 
@@ -74,10 +73,8 @@ int main()
          (unsigned) sizeof(b), ((unsigned) &b) & 0xF);
   printf("bb: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(bb), ((unsigned) &bb) & 0xF);
-#if 0
   printf("bbb: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(bbb), ((unsigned) &bbb) & 0xF);
-#endif
   printf("c: size = %u, address mod 16 = %u\n",
          (unsigned) sizeof(c), ((unsigned) &c) & 0xF);
   printf("d: size = %u, address mod 64 = %u\n",