fix(build): set CGO_ENABLED=0 in Makefile to produce static gcluster binary

[Neelabh94]

Description

The official gcluster Linux amd64 release binary (v1.102.0) fails on Debian 11 (Bullseye) due to missing GLIBC symbols:

/gcluster: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /gcluster)
/gcluster: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by /gcluster)

Root Cause

1. In PR Go version updated to the 1.26 #6173 and Provision go 1.26 cloud build infrastructure #6174 (Go 1.26 upgrade), build environments were updated to golang:1.26-trixie (Debian 13 Trixie, which has GLIBC 2.40+).
2. When building for linux/amd64 on a linux/amd64 builder host, Go defaults to CGO_ENABLED=1, dynamically linking gcluster against the builder's glibc (Debian Trixie) and embedding requirements for GLIBC_2.32 and GLIBC_2.34. Debian 11 ships with GLIBC 2.31.
3. In contrast, .github/workflows/os-support-validation.yml explicitly builds with CGO_ENABLED=0 go build -o gcluster ., which is why PR CI passed on debian:11-slim while release binaries were dynamically linked.

Solution

Explicitly set CGO_ENABLED=0 in the Makefile for the gcluster target. This ensures that:

• All Linux amd64 binaries built via make (including Cloud Build release pipelines and local builds) are fully static ELF executables with zero GLIBC dependencies.
• Binaries run portably on older Linux distributions like Debian 11, CentOS, RHEL, and minimal container environments.

Testing

• Verified make gcluster produces a statically linked ELF executable (file gcluster).
• Verified execution of ./gcluster --version inside a clean debian:11 container.
• Full test suite passed with CGO_ENABLED=0 go test ./cmd/... ./pkg/....
• Pre-commit hooks passed cleanly.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a runtime failure in the gcluster binary on older Linux distributions caused by dynamic linking against newer GLIBC versions. By forcing a static build, the change ensures portability across various environments and aligns the Makefile build process with the existing CI validation logic.

Highlights

• Static Binary Compilation: Updated the Makefile to explicitly set CGO_ENABLED=0 when building the gcluster binary.
• Compatibility Improvement: Ensures the binary is statically linked, resolving GLIBC version dependency issues on older Linux distributions like Debian 11.

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[gemini-code-assist]

Code Review

This pull request updates the Makefile to build the gcluster binary with CGO_ENABLED=0, ensuring a statically linked binary. There are no review comments to evaluate, and I have no additional feedback to provide.