Fix a bunch of warnings

[lhchavez]

This change fixes a bunch of warnings that were discovered by compiling
with clang -target=i386-pc-linux-gnu.

[lhchavez]

This intrinsic handles whatever sizes you throw at it: https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

But with some odd flag combinations in clang, it requires linking against compiler-rt, which was suboptimal. Keeping the chunk in L58-L63 avoided that case and compiled correctly with the intrinsics in all cases I could think of.

[ethomson]

Thanks for doing this - there's a lot of unrelated changes in this first commit, and they're not well described, so I'll need a little bit of time to tease things out (ugh all the different printf format descriptors). It looks correct from first glance, and I know the compiler agrees, but I'd just like to have one more set of eyes on it.

That's not meant as a complaint as much as a warning that I'll need some more time to look at this before I merge this, even though it's a rather small PR.

[lhchavez]

Moved the intrinsics part of the change to #4929 to make it easier to review.

[ethomson]

This shouldn't be necessary, Id should be 32-bit on 32-bit platforms and 64-bit on 64-bit platforms. It should be the moral equivalent of zd. From MSDN:

The ptrdiff_t and size_t types are __int32 or unsigned __int32 on 32-bit platforms, and __int64 or unsigned __int64 on 64-bit platforms. The I (uppercase i), j, t, and z size prefixes take the correct argument width for the platform.

[lhchavez]

Added a comment.

[ethomson]

Appreciate you bumping the intrinsics out, that's definitely helpful for reviewing. I think that the printf formatter values need not change to be I64 - were you seeing a warning from those that I'm not seeing immediately?

[lhchavez]

Yes, on Windows (amd64; MinGW):

2019-01-09T01:28:57.4190283Z D:\a\1\s\src\cache.c: In function 'git_cache_dump_stats':
2019-01-09T01:28:57.4190460Z D:\a\1\s\src\cache.c:51:9: warning: format '%u' expects argument of type 'unsigned int', but argument 3 has type 'size_t' {aka 'long long unsigned int'} [-Wformat=]
2019-01-09T01:28:57.4190545Z   printf("Cache %p: %"PRIuZ" items cached, %"PRIdZ" bytes\n",
2019-01-09T01:28:57.4190613Z          ^~~~~~~~~~~~~
2019-01-09T01:28:57.4190657Z    cache, git_cache_size(cache), cache->used_memory);
2019-01-09T01:28:57.4190696Z           ~~~~~~~~~~~~~~~~~~~~~

this goes away with the formatting change. let me add a comment.

[ethomson]

Cool, thanks for doing this. Looks good to me.