Fix glibc 2.34 ABI omission (missing GLIBC_2.34 in dynamic loader)

Fix glibc 2.34 ABI omission (missing GLIBC_2.34 in dynamic loader)

The glibc 2.34 release really should have added a GLIBC_2.34
symbol to the dynamic loader. With it, we could move functions such
as dlopen or pthread_key_create that work on process-global state
into the dynamic loader (once we have fixed a longstanding issue
with static linking).  Without the GLIBC_2.34 symbol, yet another
new symbol version would be needed because old glibc will fail to
load binaries due to the missing symbol version in ld.so that newly
linked programs will require.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>