Consider reducing the number of attributes in or sharding sh_posix_toolchain

[michajlo]

See also bazelbuild/bazel#10953

sh_posix_toolchain has 180 attributes, which wound up breaking Bazel's attempt to cap the number of attributes per rule-class at (what we thought was a generous) 150: bazelbuild/bazel@b839a51. It was easy enough to raise the limit to accommodate sh_posix_toolchain in this case, but it won't always be that way due to misc implementation details.

Please consider if this rule really needs so many attributes. Capping growth will ensure this rule's continued viability. Reducing attributes will help reduce outliers, which helps us better optimize for the common case.

[aherrmann]

sh_posix_toolchain has one attribute per available command

rules_sh/sh/posix.bzl

Lines 13 to 14 in 0c274ad

	# List of Unix commands as specified by IEEE Std 1003.1-2008.
	# Extracted from https://en.wikipedia.org/wiki/List_of_Unix_commands.

It should be possible to change this to a single string_dict attribute instead.

[smelc]

rules_nixpkgs's nixpkgs.bzl must be updated accordingly when this change is performed, as it depends on sh_posix_toolchain prototype: https://github.com/tweag/rules_nixpkgs/blob/451876c1521612409d83865166cfdcb5dc7fcb0c/nixpkgs/nixpkgs.bzl#L507-L511