libpthread: Test pthread stubs in threaded vs non-threaded programs.

PR lib/59685: libcrypto should not depend on libpthread

ld.elf_so: Test dynamic-then-static abuse via ctor.

XXX pullup-10

ld.elf_so: Test another edge case of mismatched TLS models.

One library defines a symbol and _doesn't_ use it, so it has no
indication of whether the symbol is for static TLS or dynamic TLS,
and then two other libraries use it in different ways.

XXX pullup-10

ld.elf_so: Test TLS abuse of static def, dynamic use and vice versa.

XXX pullup-10

ld.elf_so: Test extern dynamic TLS too.

XXX pullup-10

ld.elf_so: New test for extern initial-exec TLS, PR toolchain/50277.

XXX pullup-10

branches: 1.11.8; 1.11.18;
Implement __cxa_thread_atexit and __cxa_thread_atexit_impl. This
functions are used for destructors of thread_local objects.

If a pending destructor exists, prevent unloading of shared objects.
Introduce __dl_cxa_refcount interface for this purpose. When the last
reference is gone and the object has been dlclose'd before, the
unloading is finalized.

Ideally, __cxa_thread_atexit_impl wouldn't exist, but libstdc++ insists
on providing __cxa_thread_atexit as direct wrapper without further
patching.

branches: 1.10.8;
Update some of the set lists to use the compatdir/compatfile
compattestsdir/compattestsfile as well the kmod auto-entry creation.
Remove entries that are now instantiated by the above.

Add basic support for indirect functions. It allows providing a public
function symbol with an implementation choosen at run time.
Refactor calls to functions by address in ld.elf_so to create temporary
function descriptors on the stack, if the address is not leaked outside.

Limitations:
- no support for initialising static storage with function pointers
- no support for unnamed resolver functions

Inspired by FreeBSD's r228435 by kib@freebsd.org.

Sort entries in strcmp order.

Add a new "debug" set that gets built when ${MKDEBUG} is set. On evbarm:
-rw-r--r-- 1 root src 35806068 Jan 16 10:47 base.tgz
-rw-r--r-- 1 root src 57374069 Jan 16 10:48 comp.tgz
-rw-r--r-- 1 root src 101286193 Jan 16 10:49 debug.tgz
...
This allows always building the debugging code and libraries but not
installing it (although now it is placed in the default sets if ${MKDEBUG}
is set

branches: 1.6.2; 1.6.8;
PR/45015: ld.elf_so: support ELF symbol versioning
Applied latest patch.

fix a lot of different issues (doesn't anyone build anymore)
- libdns had the wrong version
- zfs attributes missing
- missing debug libs
- typos in library names
- typos in library versions
- _g libraries missing for new .so files (since we don't install .a files
we should not be installing _g.a files either, why are we?)
Hopefully this will fix the sparc64 build.

Move the recently added tests for libexec/ld.elf_so to shl.mi, so that
the sun2 port builds again.

Put tests depending on dlopen etc. under a test for MKPIC, and move
the corresponding entries in the set lists over to the shl.mi file.
This should bring the sun2 port back to a buildable state.

Cleanup, sort entries and remove some duplicates.

Move shared library bits of the tests out to shl.mi, so that sun2,
which only does static linking, can complete the build.