Check and document LINKER_LIST_ALIGN value for SANDBOX

LINKER_LIST_ALIGN is currently set to 32 for SANDBOX builds, not to 4 or 8 which would seem natural for 32- and 64-bit sandbox, respectively. The description for commit 0b2fa98a ("linker_lists: Fix alignment issue") does contain some interesting information but does not explain why 32 is required. This value should be checked and documented properly.

This issue is created as suggested in https://patchwork.ozlabs.org/comment/3389222/.

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