TAP build and isolated test infra fail on arm64 build containers and macOS hosts

Summary

Four independent problems stop the TAP tests from being built and run on an arm64 (aarch64) Linux build container or from a macOS host with Docker Desktop. CI runs on x86_64 Linux and hits none of them. Each needed a local workaround while working on #5905.

1. libtap.so fails to link on aarch64: vendored curl is not built with -fPIC

/usr/bin/ld: .../deps/curl/curl/lib/.libs/libcurl.a(libcurl_la-cfilters.o): relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `Curl_cf_def_cntrl' which may bind externally can not be used when making a shared object; recompile with -fPIC
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:107: libtap.so] Error 1

deps/Makefile passes CFLAGS=-fPIC as an environment variable to curl's make. The Makefile generated by configure assigns CFLAGS itself, so the value is ignored and libcurl.a contains non-PIC objects. x86_64 tolerates this when linking libtap.so; aarch64 does not.

2. TAP test link requires the system libzstd

/usr/bin/ld: cannot find -lzstd: No such file or directory

On Linux, test/tap/tests/Makefile, test/tap/tests/unit/Makefile and test/deps/cluster_simulator/Makefile link -Wl,-Bdynamic -lzstd, which needs the distribution's libzstd-dev. The proxysql/packaging:build-* images do not ship it, while the proxysql binary already links the vendored deps/zstd/zstd/lib/libzstd.a.

3. SKIP_CLUSTER_START=1 times out on macOS hosts

>>> Starting ProxySQL container: proxysql.dev-... (cluster nodes: 0)
Waiting for proxysql.dev-...:6032 .. Ready.
Waiting for proxy-node1 (port 6042) .............................. TIMEOUT (node 1)

Host-side infra scripts loop with $(seq 1 "${NUM_NODES}"). GNU seq 1 0 prints nothing, but BSD seq on macOS counts down and prints 1 0.

4. Re-running start-proxysql-isolated.bash aborts on macOS hosts

chmod: changing permissions of './pgsql-sockets/.s.PGSQL.5432': Invalid argument

The script runs chmod -R 777 over ci_infra_logs/<INFRA_ID> in a helper container. That directory holds the PostgreSQL socket shared with the backend, and Docker Desktop file sharing rejects chmod on a socket. With set -e the script exits. This breaks the documented way to swap in a rebuilt binary without tearing down the backends.

Environment

• Host: macOS (arm64), Docker Desktop 29.7.2, linux/arm64 VM
• Build image: proxysql/packaging:build-debian12-v4.0.0
• Branch: v3.0 (594ed7cd3)

Not included

test/tap/groups/test_makefile_dependencies.py fails 3 checks when run directly on macOS, because the system GNU Make 3.81 does not support the private target-specific modifier. It passes with GNU Make 4.3, and run-ci-lint.bash runs it on Linux in CI, so no change is proposed for that.