Now that VST3 builds are signed before and after manifest generation, it
may be necessary to force-sign in order to overwrite the
previously-applied signature.

To prevent too much disruption to people who have our public projects as
part of their build or testing systems we are temporarily ignoring a
warning about using Xcode 15.

Co-authored-by: Roland Rabien <figbug@gmail.com>

This reverts commit 82377a787a.

Reintegrates changes from cf9fc84669

Similar code was incorrectly removed in
070a6b35e9.

When using CLion to invoke CMake, using a Clang toolchain and Ninja, and
targeting x64, CLion will pass -m64 in CMAKE_C_FLAGS and
CMAKE_CXX_FLAGS. The compilers are passed through to the juceaide build,
but the target arch was not, which meant that the linker attempted to
link x86 libraries, which failed.

This fixes an issue where the app icon would not be visible for
standalone plugin targets.