The legacy mode was using the new nativeKey to create a semaphore.
As a result, on macOS the name of the semaphore key file was the same
as the name of the shared memory key file.
This lead to a situation when the file was mistakenly deleted when
destroying any instance of the shared memory, not only the one that
created it.
Fix it by using QSystemSemaphore::legacyNativeKey() in legacy mode.
Add a test to verify that we cannot re-create a shared memory with the
same key. The test was failing on macOS without the fix.
Fixes: QTBUG-111855
Pick-to: 6.6
Change-Id: Ib0bc41791e889b1888bbb8aa9044c6b053b63a5a
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
02c42b26e1