libc: add memset test for int-to-char conversion

[strajabot]

Summary

Test case to check if an implementation of memset correctly
handles the value passed being wider than a byte

[strajabot]

Larger buffer size better tests how the parameter is handled

[fuz]

Test looks reasonable. Were you able to trigger test suite failure with your broken memset?

lib/libc/tests/string/memset_test.c

6–26

No need to put the full license text in if you already have a SPDX identifier.

[strajabot]

Yes, the test fails with the broken memset, and passes with the fixed version

[strajabot]

Leave only the SPDX identifier and copyright

[fuz]

Looks reasonable. Still needs approval from a src committer.

[emaste]

Approved with a tiny style change that can be applied

lib/libc/tests/string/memset_test.c

18

style(9) wants spaces -- for (int i = 0; i < 64; i++) {