[AIX][TLS] Produce a faster local-exec access sequence for the "aix-small-tls"...

[AIX][TLS] Produce a faster local-exec access sequence for the "aix-small-tls" global variable attribute (#83053)

Similar to 3f46e545, this patch allows
the backend to produce a faster access sequence for the local-exec TLS
model, where loading from the TOC can be avoided, for local-exec TLS
variables that are annotated with the "aix-small-tls" attribute.

The expectation is for local-exec TLS variables to be set with this
attribute through PGO. Furthermore, the optimized access sequence is
only generated for local-exec TLS variables annotated with
"aix-small-tls", only if they are less than ~32KB in size.