Non-hardcoded `_gp` value support #125

Job	Run time
Check format	7s
Run tests	30s
Check clippy	26s
msrv	2m 49s
Publish	37s
release artifact for x86_64-pc-windows-gnu	1m 41s
release artifact for x86_64-pc-windows-msvc	1m 19s
release artifact for x86_64-apple-darwin	1m 34s
release artifact for aarch64-apple-darwin	1m 42s
release artifact for x86_64-unknown-linux-musl	38s
release artifact for x86_64-unknown-linux-gnu	36s
	11m 59s

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