AIX: Fix executable ENABLE_EXPORTS in Makefile generators

In commit afcd9fe669 (AIX: Add an option to disable automatic exports
from shared libraries, 2020-01-30, v3.17.0-rc1~47^2) the population of
the `<AIX_EXPORTS>` rule variable placeholder was accidentally added to
the device linking rule rather than the main linking rule.  This caused
our `ExportImportList` script on AIX, when called for executables with
`ENABLE_EXPORTS` set, to be given an `AIX_EXPORTS` file name that does
not exist, leading to a warning from the `dump` tool.

Move the population of the `<AIX_EXPORTS>` placeholder in the Makefile
generators to the main link rule.

Issue: #20290
1 file changed