request: add fmodf for x86_64-unknown-uefi

[gshep]

Hello! I tried to use several math crates in a sample for x86_64-unknown-uefi and encountered the following issues:

1. libm - requires __truncdfsf2. There is already an issue for it = Missing __truncdfsf2 for aarch64-unknown-none-softfloat #327
2. micromax - requires fmodf. I created an issue in the project's repo (rust-lld: error: undefined symbol: fmodf tarcieri/micromath#95) but the author suggested me to request it here. The build error log can be found there.
3. https://github.com/nagisa/math.rs - requires both fmodf & __trunsdfsf2.

So I would like fmodf be added to the builtins. Thanks in advance!

[bjorn3]

fmodf already exists in the libm crate: https://github.com/rust-lang/libm/blob/master/src/math/fmodf.rs It is only included by compiler-builtins on wasm32-unknown-none, baremetal arm and the fortanix sgx environment though:

compiler-builtins/src/lib.rs

Lines 45 to 50 in e6fd1b2

	#[cfg(any(
	all(target_arch = "wasm32", target_os = "unknown"),
	all(target_arch = "arm", target_os = "none"),
	all(target_vendor = "fortanix", target_env = "sgx")
	))]
	pub mod math;

[gshep]

Then I'd like it to be enabled for x86_64-unknown-uefi =)

[Amanieu]

I'd be happy to accept a PR, I think you only need to add a line to that cfg block @bjorn3 linked to.