Use build-std-features instead of rlibc

[YtvwlD]

I've built a UEFI application with this library this year and it worked great, thank you!

But there's one thing I've noticed in the test-runner and in the application template:

uefi-rs/uefi-test-runner/Cargo.toml

Lines 14 to 17 in 229da01

	# When building using Cargo's `build-std` feature, the `mem` feature of `compiler-builtins`
	# does not automatically get enabled. Therefore, we have to manually add support for
	# the memory functions.
	rlibc = "1.0.0"

So, I wondered, why not directly enable the mem feature of compiler-builtins? It seems to work both in my application and in the test-runner, so I thought, I'd submit this as a PR. If there's something I'm missing, feel free to close this PR. :)

There's one last thing about the BUILDING.md I stumbled upon while creating this PR, but it's not really important:

uefi-rs/BUILDING.md

Line 27 in d289e0c

Cargo feature: `cargo +nightly build -Z build-std --target x86_64-unknown-uefi`.

Why is the command line that long? -Z build-std is already specified in .cargo/config, so it's not really needed. (The same applies to -Z build-std-features=compiler-builtins-mem.)

[YtvwlD]

I guess this error is not my fault. It also occurs with the current nightly compiler on master.
With nightly-2021-10-07, 08 and 09, the tests work.

[nicholasbishop]

I think you are correct that this command is unnecessarily long, could you change it to just cargo +nightly build --target x86_64-unknown-uefi?

[nicholasbishop]

Thanks for the PR! I don't know about the history of why that wasn't previously in .cargo/config, but I think this looks like a nice simplification. Left one comment on BUILDING.md but otherwise looks good.

I guess this error is not my fault. It also occurs with the current nightly compiler on master.

Confirmed, that's #299. I disabled the failing test for now though so tests should pass if you rebase.

[nicholasbishop]

Looks good, thanks!