[clang-tidy] Add checker for operations between integrals and pointers

[clang-tidy] Add checker for operations between integrals and pointers

Summary:
This check is finding suspicious operations involving pointers and integral types; which are most likely bugs.

Examples:
subversion/v1_6/subversion/libsvn_subr/utf.c
```
static const char *
fuzzy_escape(const char *src, apr_size_t len, apr_pool_t *pool)
{
  [...]
   while (src_orig < src_end)
    {
      if (! svn_ctype_isascii(*src_orig) || src_orig == '\0')   // Should be *src_orig
        {
```

apache2/v2_2_23/modules/metadata/mod_headers.c
```
static char *parse_format_tag(apr_pool_t *p, format_tag *tag, const char **sa)
{
  [...]
    tag->arg = '\0';   // ERROR: tag->arg has type char*

    /* grab the argument if there is one */
    if (*s == '{') {
        ++s;
        tag->arg = ap_getword(p,&s,'}');
    }
```

Reviewers: alexfh

Subscribers: Eugene.Zelenko, cfe-commits

Differential Revision: http://reviews.llvm.org/D19118

llvm-svn: 266450