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.

When building for arm64 with a VS generator on a x86_64 host,
CMAKE_CROSSCOMPILING is not set, and copying the generator platform can
result in a juceaide binary that doesn't run on the host system.

The removed code no longer seems to be necessary when configuring with
newer Clion versions.

This issue made hosts not recognize the ARA capabilities of AU plugins.

AU and AUv3 plugins only support version numbers with up to 3 parts.

This change allows multiple versions of JUCE to be installed to the same
CMAKE_INSTALL_PREFIX, avoiding conflicting paths to juceaide.

This change helps to avoid ambiguity in includes when building projects
which contain more than one "BinaryData.h".

Once JUCE has been built, you can use the following line to include
the targets from the build tree (replace `JUCE_BUILD_DIR` as
appropriate).
```
include("${JUCE_BUILD_DIR}/JUCEExportConfig.cmake")
```