feat(thread): futex + TLS + pthread_self substrate

Makefile.am

@@ -73,6 +73,10 @@ VLIBC_CORE_SRCS = \
     src/start/exit.c \
     src/start/environ.c \
     src/start/tls.c \
+    src/thread/futex.c \
+    src/thread/pthread_self.c \
+    src/thread/tls.c \
+    src/thread/x86_64/__set_thread_area.s \
     src/errno/strerror.c \
     src/setjmp/x86_64/setjmp.s \
     src/setjmp/x86_64/longjmp.s \
@@ -693,6 +697,7 @@ EXTRA_DIST = \
     arch/x86_64/syscall_arch.h \
     src/internal/atomic.h \
     src/internal/errno.h \
+    src/internal/futex.h \
     src/internal/libc.h \
     src/internal/malloc.h \
     src/internal/strtox.h \
@@ -700,6 +705,7 @@ EXTRA_DIST = \
     src/internal/types.h \
     src/start/start.h \
     src/start/tcb.h \
+    src/thread/pthread_impl.h \
     src/dirent/dirent_impl.h \
     src/process/atfork_impl.h \
     src/stat/stat_impl.h \