[llvm] [llvm-strings] Use small buffer instead of reading whole file (PR #163073)

[James Henderson via llvm-commits]

jh7370 wrote:

> The previous and current experiments were both run for 5 rounds, and I used the median result. All results are within ±0.1 seconds.
> 
> Previously, I used a 1 GB random file generated with `dd if=/dev/random`. This time, I am using a freshly built Clang binary for the test, which is about 1.8 GB.

Thanks. So we just need the Windows performance figures and I think this is otherwise good from my point of view.

https://github.com/llvm/llvm-project/pull/163073