PR35503 - warn for restrict pointer

[Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>]

Hi,
The following patch adds option -Wrestrict that warns when an argument
is passed to a restrict qualified parameter and it aliases with
another argument.

eg:
int foo (const char *__restrict buf, const char *__restrict fmt, ...);

void f(void)
{
  char buf[100] = "hello";
  foo (buf, "%s-%s", buf, "world");
}

With the patch, C FE warns:
test-3.c: In function ‘f’:
test-3.c:6:3: warning: passing argument 1 to restrict qualified
parameter aliases with argument 3

   foo (buf, "%s-%s", buf, "world");
   ^~~

However with C++FE it appears TYPE_RESTRICT is not set for the
parameters (buf and fmt)
and hence the warning doesn't get emitted for C++.
C FE sets TYPE_RESTRICT for them. I am not sure how to workaround this
issue, and would be grateful for suggestions.

Thanks,
Prathamesh

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