Update NEWS and NEWS.ja for Yash 2.61 unreleased changes

[Copilot]

Documents four recently merged contributions in the Yash 2.61 (Unreleased) changelog sections of both NEWS (English) and NEWS.ja (Japanese).

Entries added

• Cross-compilation support (Support cross compiling #203): configure now accepts --host=HOST to set the toolchain prefix for cross-compilation targets.
• -fno-builtin fix (build function checks with -fno-builtin #201): configure function-availability checks could produce false positives when an optimizing compiler eliminated test code; function check programs are now compiled with -fno-builtin.
• fork_and_wait bug fix (Add a missing else in fork_and_wait() #221): Missing else in fork-result branching could cause incorrect behavior on fork failure.
• New completions (Add completion for 'mount', 'sv', 'aria2c', 'mkinitcpio', '7z', 'hdparm' #230): Added line-editing completions for mount, sv, aria2c, mkinitcpio, 7z, and hdparm.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update NEWS</issue_title>
<issue_description>- [ ] #201

• Support cross compiling #203
• Add a missing else in fork_and_wait() #221
• Add completion for 'mount', 'sv', 'aria2c', 'mkinitcpio', '7z', 'hdparm' #230</issue_description>

<agent_instructions>Update the NEWS and NEWS.ja files to reflect changes listed in the description of this issue.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Update NEWS #211

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[magicant]

reworked in #232