Swift: honour `IMPLIB_LOCATION` property

The rules did not account for the import library location (through
`<TARGET_IMPLB>`) and instead would always write the import library to
the default location (next to the shared library/executable).  This
prevented the use of `CMAKE_RUNTIME_OUTPUT_LOCATION` and
`CMAKE_ARCHIVE_OUTPUT_LOCATION`.
39 jobs for swift-import-library-location
Status Job ID Name Coverage
  External
passed cdash

passed cmake-dash3win10-windows-release-ninja

passed cmake-hythloth-linux-debug-makefiles+sphinx

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-release-makefiles

passed cmake-terfin-windows-release-vs2019

passed ghostflow-check-master

passed ghostflow-stager

passed cdash

passed cdash

failed cmake-dash3win10-windows-release-ninja

00:17:44

failed cmake-dash3win10-windows-release-ninja

passed cmake-dash3win10-windows-release-ninja

00:16:26

passed cmake-hythloth-linux-debug-makefiles+sphinx

00:41:04

passed cmake-minoc-linux-release-lint-iwyu-tidy

00:11:05

passed cmake-moonshade-osx-debug-ninja

00:17:01

passed cmake-moonshade-osx-release-makefiles

00:10:28

passed cmake-terfin-windows-release-vs2019

00:48:44

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager