Set/Enforce Minimum supported macOS version

[xavier2k6]

qBittorrent & operating system versions

qBittorrent: 4.x/master
OS: macOS

What is the problem?

In below PR, a Min. macOS version was set:

• Set correct minimum macOS version with CMake #14813

However it seemed that this PR may have not fully done what it was intended to do. See #19066 (comment)

---

In below PR, QMake Support was removed in master

• Drop support of Autoconf/Automake and QMake #19335

• Now, there's no set minimum for macOS in master & we need to review/correctly set this.
  

  qBittorrent/src/app/CMakeLists.txt

  Lines 91 to 92 in 7786e1b

  	# This variable name should be changed once qmake is no longer used. Refer to the discussion in PR #14813
  	set(MACOSX_DEPLOYMENT_TARGET ${CMAKE_OSX_DEPLOYMENT_TARGET})

Steps to reproduce

No response

Additional context

No response

Log(s) & preferences file(s)

No response

[sledgehammer999]

The Qt docs say that Qt sets the minimum required target to CMAKE_OSX_DEPLOYMENT_TARGET.
Reading the whole thread in #14813 it seems that this:

set(MACOSX_DEPLOYMENT_TARGET ${CMAKE_OSX_DEPLOYMENT_TARGET})

is required for substituting the MACOSX_DEPLOYMENT_TARGET in the Info.plist file. They were forced to leave that var name for compatibility reasons with qmake. Now that qmake is gone, the var name should be changed to something else because the same var name is also used by cmake itself to derive CMAKE_OSX_DEPLOYMENT_TARGET (and this leads to confusion to readers).