Update m4-version to 1.4.21 from 1.4.19

[zosopentoolsmain]

No description provided.

[sachintu47]

augment review

[augmentcode]

🤖 Augment PR Summary

Summary: Updates the port to track the GNU m4 1.4.21 stable release and refreshes the z/OS-specific stable patch set.

Changes:

• Bumped M4_VERSION from 1.4.19 to 1.4.21 and updated the stable download URL accordingly.
• Adjusted STABLE build dependencies (notably adding texinfo and coreutils).
• Removed the prior “PR1” header-shim include files previously carried under stable-patches/PR1/include.
• Removed older stable patch files (e.g., prior configure/canonicalize/doc patches) and consolidated to a new stable-patches/builtin.c.patch.
• Updated the stable builtin.c patch to tag file descriptors as ASCII on z/OS using __chgfdccsid (via <zos.h>) for child I/O and temporary files.
• Moved/pruned stable patch documentation by renaming stable-patches/PR2/README.md to stable-patches/README.md and dropping notes for removed patches.

Technical Notes: The stable patch set now depends on z/OS charset tagging support (__CHARSET_LIB) and uses <zos.h>/__chgfdccsid to ensure ASCII tagging when running child processes and creating temporary files.

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[augmentcode]

Review completed. 3 suggestions posted.

Comment augment review to trigger a new review at any time.

[augmentcode]

ZOPEN_STABLE_DEPS no longer includes anything that would obviously provide <zos.h>, but the STABLE patch set now includes stable-patches/builtin.c.patch which adds that header. Can you confirm the STABLE build environment reliably has the needed header (e.g., via zoslib) so the build won’t fail on missing includes?

Severity: medium

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[augmentcode]

This PR removes the PR1 header-shim includes, but buildenv’s STABLE path still sets -I${ZOPEN_ROOT}/patches/PR1/include in ZOPEN_EXTRA_CFLAGS. Can you confirm the STABLE build no longer depends on that include directory (or that it’s still generated elsewhere), otherwise headers may regress or the include path may go stale?

Severity: medium

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[augmentcode]

stable-patches/builtin.c.patch introduces an unconditional #include <zos.h> in the upstream source. Is it guaranteed that this patch is only applied/compiled in environments where zos.h exists (and not, e.g., during any non-z/OS validation builds), since the include isn’t guarded by __MVS__?

Severity: low

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[HarithaIBM]

LGTM