Populate environment for macOS builds

[fmeum]

While trying to set up rules_graalvm@HEAD within Bazel itself in bazelbuild/bazel#19361, I ran into CI failures on macOS due to the missing environment variable DEVELOPER_DIR (see https://buildkite.com/bazel/bazel-bazel-github-presubmit/builds/17182#018a41ad-4977-4468-b1ab-523f0710e4ad/513-543).

Could rules_graalvm be missing a call to apple_common.target_apple_env or, probably even better, apple_support.run?

[sgammon]

@fmeum We are definitely missing such calls. So far, the only way I know to initialize the Xcode environment is to pass those variables through from the default_shell_env:

rules_graalvm/internal/native_image/rules.bzl

Lines 188 to 197 in aad2b28

	if (not ctx.attr._legacy_rule):
	for var in _PASSTHRU_ENV_VARS:
	if var == "DEVELOPER_DIR" and unix_like:
	# allow bazel to override the developer directory on mac
	env[var] = apple_common.apple_toolchain().developer_dir()
	elif var == "SDKROOT" and unix_like:
	# allow bazel to override the apple SDK root
	env[var] = apple_common.apple_toolchain().sdk_dir()
	elif var in ctx.configuration.default_shell_env:
	env[var] = ctx.configuration.default_shell_env[var]

If you know how to prepare the Apple toolchain, I'd love some advice on this topic, or I would be happy to accept a PR. I have a doc with hermetic compile advice (to the best of my knowledge, of course), and it recommends setting BAZEL_USE_CPP_ONLY_TOOLCHAIN=1 which isn't ideal. So I can update that too.

I'll take a look these links you've shared to absorb the docs.

Also, thanks for using the rules and for reporting your experience.