D27429: ThreadWeaver: Convert license headers to SPDX expressions

[Andreas Cord-Landwehr]

cordlandwehr added a task: T11550: Add SPDX License markers.

REPOSITORY
  R279 ThreadWeaver

REVISION DETAIL
  https://phabricator.kde.org/D27429

To: cordlandwehr
Cc: kde-frameworks-devel, mirko, LeGast00n, cblack, GB_2, michaelh, ngraham, 
bruns