Fix macos bundle

[hmueller01]

Fixed a few things to make build work on macOS.

[novomesk]

Hello @s-daveb ,

You tried to build nomacs on MacOS in the past.
Would you like to test these changes and tell me if you agree with them.

[s-daveb]

The first make call failed unless I ran export CPLUS_INCLUDE_PATH=/usr/local/include before make.

Then it subsequently built, but the second call to make bundle failed with:

[100%] Linking CXX executable nomacs.app/Contents/MacOS/nomacs
[100%] Built target nomacs
build ❯ make bundle                                                                              master
CMake Error at bundle.cmake:17 (file):
  file COPY cannot find "/Resources/qt_menu.nib": No such file or directory.

[hmueller01]

The first point is documented in the README.md. I hope you've seen this.

The second failure this is really strange. Did you really checkout this branch?
make bundle shouldn't use bundle.cmake at all, as I replaced this target by macdeployqt

get_target_property(_qmake_executable Qt5::qmake IMPORTED_LOCATION)
get_filename_component(_qt_bin_dir "${_qmake_executable}" DIRECTORY)
find_program(MACDEPLOYQT_EXECUTABLE macdeployqt HINTS "${_qt_bin_dir}")

add_custom_target(bundle
	COMMAND ${MACDEPLOYQT_EXECUTABLE} ${BINARY_NAME}.app -dmg
	DEPENDS ${BINARY_NAME}
	COMMENT "Execute ${MACDEPLOYQT_EXECUTABLE} to create macOS bundle")

at the end of MacBuildTarget.cmake.

The whole command should look like this (if nomacs.app and nomacs.dmg are not yet created):

> make bundle
[  1%] Automatic MOC for target nomacsCore-3.17.0
[  1%] Built target nomacsCore-3.17.0_autogen
[ 60%] Built target nomacsCore-3.17.0
[ 61%] Automatic MOC for target nomacs
[ 61%] Built target nomacs_autogen
[ 98%] Built target nomacs
[100%] Execute /usr/local/opt/qt5/bin/macdeployqt to create macOS bundle
[100%] Built target bundle