[dlfcn] E: Add tests for ctors/dtors and DT_RUNPATH

[esaurez]

Summary

Add a new test suite dlfcn-init-runpath-c that exercises the three System V ABI capabilities the Nanvix dynamic loader now implements (esaurez/nanvix#27):

1. .init_array constructor invocation on dlopen
2. .fini_array destructor invocation on dlclose
3. DT_RUNPATH-driven DT_NEEDED resolution

Test design

• libctor.so — has __attribute__((constructor)) writing a sentinel to a library-local global, and __attribute__((destructor)) writing a different sentinel to the test program's extern volatile int g_dtor_ran (exported by -rdynamic). The destructor witness survives the library being unloaded because the global lives in the main executable.
• libparent.so — linked with -lchild -Wl,--enable-new-dtags,-rpath,lib/subdir. The linker emits DT_NEEDED libchild.so plus DT_RUNPATH lib/subdir.
• libchild.so — staged into lib/subdir/ only (never lib/) via SUITE_RAMFS_LIBS. The only way the loader can find it is by honouring libparent's DT_RUNPATH.

Hooks

File	Change
src/dlfcn-init-runpath-c/{Makefile,main.c,libs/*}	New suite
Makefile, src/Makefile	Register dlfcn-init-runpath-c in SUITES
.nanvix/z.py	Register suite in ALL_SUITES, STANDALONE_ONLY_SUITES, and SUITE_RAMFS_LIBS (the latter stages libchild.so under lib/subdir/)

Validation

Run on a standalone Nanvix VM with the loader changes from esaurez/nanvix#27:

RUN  dlfcn-init-runpath-c...
=== dlfcn init_array + DT_RUNPATH tests ===
  PASS: init_array fires on dlopen
  PASS: fini_array fires on dlclose
  PASS: DT_RUNPATH dependency search

3 passed, 0 failed
OK   dlfcn-init-runpath-c
        *** POSIX tests PASSED ***

All 15 testable suites pass (the new suite plus the 14 pre-existing ones).

ELF metadata sanity check

$ readelf -d build/libparent.so | head -4
 0x00000001 (NEEDED)                     Shared library: [libchild.so]
 0x0000001d (RUNPATH)                    Library runpath: [lib/subdir]

$ readelf -d build/libctor.so | grep -E "INIT_ARRAY|FINI_ARRAY"
 0x00000019 (INIT_ARRAY)                 0x1188
 0x0000001b (INIT_ARRAYSZ)               4 (bytes)
 0x0000001a (FINI_ARRAY)                 0x118c
 0x0000001c (FINI_ARRAYSZ)               4 (bytes)

Companion PR

esaurez/nanvix#27 — the loader changes this suite exercises. This PR is unlinked-but-meaningful without it: the test would fail with "destructor sentinel not set" / "DT_RUNPATH dependency search" / "constructor sentinel not set" on an unpatched loader.

[esaurez]

Superseded by upstream PR nanvix/posix-tests#174, which carries the same test contribution -- rebased onto current upstream/main (pulled in zutils v0.11.1 from #175), deep-reviewed, validated end-to-end against the local nanvix init-array build (all 3 cases plus the full posix-tests suite pass). One MUST FIX applied: stripped a non-ASCII em-dash from main.c. One SHOULD FIX applied: added build-time readelf assertions in the suite Makefile that libctor.so contains INIT_ARRAY+FINI_ARRAY, libparent.so contains DT_NEEDED libchild.so + DT_RUNPATH lib/subdir, AND that the legacy DT_RPATH is NOT present (prevents silent regression if a future toolchain change flips --enable-new-dtags). The upstream loader companion is nanvix/nanvix#2473. Closing this fork PR; tracking continues upstream.