Fix sign conversion warnings in lfs_util.h

[toastdb]

There are a few sign conversion warnings when building with -Wsign-conversion in lfs_util.h that I'd like to resolve.

[geky-bot]

Tests passed ✓, Code: 17112 B (+0.0%), Stack: 1448 B (+0.0%), Structs: 812 B (+0.0%)

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Readonly	6230 B (+0.0%)	448 B (+0.0%)	812 B (+0.0%)	Branches	1283/1616 branches (+0.0%)
Threadsafe	17964 B (+0.0%)	1448 B (+0.0%)	820 B (+0.0%)		Benchmarks
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Error-asserts	17924 B (+0.0%)	1440 B (+0.0%)	812 B (+0.0%)	Erased	1568888832 B (+0.0%)

[geky]

Hi @toastdb, thanks for creating a PR.

Two concerns:

1. Compiling lfs.c with -Wsign-conversion results in 104 warnings. What is the use case for compiling lfs_util.h differently?

   If -Wsign-conversion can't be adopted in littlefs's Makefile this is is high-risk for regressing in the future.

2. This risks hiding legitimate type mismatches between, for example, uint32_t and __builtin_ctz, __builtin_ctzl, __builtin_ctzll, etc. due to the bluntness of C's typecasts.

[toastdb]

Hi @geky,

1. We compile our source with stricter flags than 3rd party code. Because lfs.h is included and brings in lfs_util.h the warnings pop up. I did attempt to enable the flag for the whole littlefs repo and saw resolving that would be pretty intrusive for something nobody asked for.
2. This seems like a valid concern and I'm happy to close the PR.

[geky]

We compile our source with stricter flags than 3rd party code. Because lfs.h is included and brings in lfs_util.h the warnings pop up.

Hmm, I can see where this would be annoying.

It's not the cleanest solution, but would wrapping the include with a pragma work?

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsign-conversion"
#include "lfs.h"
#pragma GCC diagnostic pop

Another option is copying lfs_util.h, applying the above patch, and using -DLFS_CONFIG=my_util.h. lfs_util.h is intended to be replaceable, though not quite for this reason.

[toastdb]

I appreciate the tips but we've got them in an ignore list, we were just trying to decrease the list.