lang/ruby*: fix runtime on powerpc64*

The hand-written coroutine_transfer in coroutine/ppc64le/Context.S
lacks the ELFv2 ABI global entry prologue. When the function is reached
via the PLT (lazy resolution path), r2 (TOC pointer) is left pointing
at whatever the resolver had loaded — typically the dynamic linker's
own TOC — instead of libruby's TOC.

The wrong r2 propagates through the fiber switch into fiber_entry,
which jumps into fiber_restore_thread → rb_current_ec_set. The
first PLT thunk inside the new fiber (__plt___tls_get_addr for the
ruby_current_ec thread-local) computes its GOT entry as
r2 + offset and segfaults dereferencing the bogus address.

Fixes build of textproc/rubygem-nokogiri and devel/rubygem-glib2.