Make `libia2` a `.so`

[kkysen]

For issues like #619 where multiple copies of globals from libia2 were conflicting, we'd like to make libia2 a .so instead of a .a, as there's no specific reason why it needs to be a .a. The contortions of definitions in #619 to have mutable globals defined in INIT_RUNTIME makes things harder to understand, so a .so is preferable. See #619 (comment).

As of #632, which makes a few functions static that should've been, liblibia2.a exports the following symbols

❯ nm -g --defined-only build/x86_64/runtime/libia2/liblibia2.a

ia2.c.o:
0000000000000050 T ia2_get_compartment
0000000000000030 T ia2_get_tag
0000000000000000 T ia2_stackptr_for_compartment
0000000000000700 T protect_pages
0000000000000210 T protect_tls_pages

init.c.o:
0000000000000060 T allocate_stack
00000000000002e0 T allocate_stack_0
0000000000000000 T ia2_get_compartment_stack
0000000000000350 T ia2_register_compartment
0000000000000310 T ia2_reinit_stack_err
0000000000000440 T ia2_start

threads.c.o:
0000000000000000 T ia2_thread_begin
00000000000000a0 T __wrap_pthread_create

main.c.o:
0000000000000000 T __wrap_main

exit.c.o:
0000000000000000 T _exit
0000000000000005 T exit

memory_maps.c.o:
0000000000000170 T ia2_addr_location_find
0000000000000340 T ia2_log_memory_maps
0000000000000000 T ia2_thread_metadata_get_for_current_thread

thread_name.c.o:
0000000000000000 T thread_name_get

[ayrtonm]

multiple copies of globals from libia2 were conflicting

Just to be super clear, the multiple copies don't cause problems since symbol references to one of these will always be resolved to the same one. Deduplicating them just makes things easier to understand.

[kkysen]

multiple copies of globals from libia2 were conflicting

Just to be super clear, the multiple copies don't cause problems since symbol references to one of these will always be resolved to the same one. Deduplicating them just makes things easier to understand.

They were causing problems with code that assumed there was a single global, but different compartments had separate copies of the singleton.