We set 'ld -z max-page-size' to 4KiB to prevent the linker from aligning
the text segment to any built-in default (e.g., 4MiB on x86_64 or 64KiB
on ARM). Otherwise, the padding bytes are wasted at the beginning of the
final binary.
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082