Export AIX TLS symbols

TLS symbols in AIX display a new, different symbol type in nm output.
Libtool explicitly creates a list of exported symbols for AIX shared
libraries using nm and does not recognize the new TLS symbols, so
those symbols are not exported in AIX shared libraries.

This is a regression for TLS support on AIX where TLS symbols or GCC
"emultls" symbols were listed as global data and exported.

This patch updates libtool.m4 export_symbols_cmds for AIX in two
locations so that global symbols labeled with "L" for TLS are included
in the export list.

* m4/libtool.m4 (export_symbols_cmds) [AIX]: Add global TLS "L" symbols.

Thanks, David