include merging

[mgood7123]

is it possible to, in future releases, have Boost for Android merge the header files of all build architectures into a single includes folder? in that, for example, when building --arch=arm64-v8a,x86_64 it will generate

build/out/merged/include/boost-1_73/boost

with

build/out/arm64-v7a/include
build/out/x86_64/include

being deleted, as to avoid gradle and other indexing systems from indexing the boost headers multiple times