pgsql: aix: No need to use mkldexport when we want to export all symbol

aix: No need to use mkldexport when we want to export all symbols

When building a shared library with exports.txt there's no need to build an
intermediary static library, we can just pass -Wl,-bE:... when generating the
.so.

When building a shared library without exports.txt, there's no need to call
mkldexport.sh to export all symbols, because all symbols are exported anyway,
and we don't need the export file on the import side (like we do for
postgres.imp).

This makes building .so's on aix a lot more similar to building on other
platforms. In particular, we don't create and remove a .a of the same name but
different contents anymore.

Discussion: https://postgr.es/m/20220820174213.d574qde4ptwdzoqz@awork3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fe6a64a58ab3e5bda3aceee2f1ee3e8efdb03865

Modified Files
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src/Makefile.shlib         | 45 ++++++++++++++++++---------------------------
src/makefiles/Makefile.aix |  8 ++------
2 files changed, 20 insertions(+), 33 deletions(-)