`-Wdeprecated-copy` found this copy-assignment operator, which it
complains about. Since it is just `= default`, we should be able to
remove both it and the default constructor, making the struct just its
data members.

Fixes #2614
Ref: https://gcc.gnu.org/gcc-12/porting_to.html

 Otherwise we get errors like this:

 CMake Error at doc/cmake_install.cmake:46 (file):
  file INSTALL cannot find
  "/<<PKGBUILDDIR>>/build/doc/html": No such file or
  directory.
 Call Stack (most recent call first):
  cmake_install.cmake:59 (include)

CMAKE_EXE_LINKER_FLAGS contains, among other things, the LDFLAGS which
many distros use to universally apply linker flags.
When completely replacing CMAKE_EXE_LINKER_FLAGS, these flags are lost.

If a script module is waiting on a non-tailed script to finish, polybar
cannot shut down until the script has terminted.
To remedy this, we use the same polling loop as for tailed scripts which
checks if it needs to terminate after every iteration.