build(deps): bump libm from 0.2.7 to 0.2.8 in /hermit-builtins #1817

Job	Run time
Build	1m 55s
Clippy	1m 33s
Check	1m 9s
Check docs	38s
Format	22s
Run (x86_64, rusty_demo, none, dev)	3m 43s
Test	1m 36s
Run Hermit for Rust (x86_64 + kvm)	4m 0s
Run (x86_64, rusty_demo, none, release)	2m 32s
Run (x86_64, httpd, virtio-net-pci, dev)	2m 53s
Run (x86_64, httpd, virtio-net-pci, release)	3m 17s
Run (x86_64, httpd, rtl8139, dev)	3m 4s
Run (x86_64, httpd, rtl8139, release)	2m 53s
Run (x86_64, testudp, virtio-net-pci, dev)	2m 52s
Run (x86_64, testudp, virtio-net-pci, release)	3m 0s
Run (x86_64, testudp, rtl8139, dev)	2m 36s
Run (x86_64, testudp, rtl8139, release)	2m 45s
Run (x86_64, hello_world, none, dev)	2m 26s
Run (x86_64, hello_world, none, release)	3m 0s
Run (aarch64, rusty_demo, none, dev)	4m 59s
Run (aarch64, rusty_demo, none, release)	2m 49s
Run (aarch64, httpd, virtio-net-pci, dev)	2m 46s
Run (aarch64, httpd, virtio-net-pci, release)	2m 58s
Run (aarch64, testudp, virtio-net-pci, dev)	3m 28s
Run (aarch64, testudp, virtio-net-pci, release)	2m 43s
	1h 5m 57s

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