Can't compile boost_libiostreams for iOS

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Hi,
I'm discovering Mason usage, so maybe I'm wrong.
I made a simple Makefile for testing purpose.
I can get geojson 0.4.0 build for iOS and the static lib has the 4 slices arm i386 etc.
But when I try the same with boost iostreams lib, it fails by building all slices for x86_64

input file lib-ios-arm64/libboost_iostreams.a is not a fat file
Non-fat file: lib-ios-arm64/libboost_iostreams.a is architecture: x86_64
* Creating Universal Binary...
fatal error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/lipo: lib-isim-i386/libboost_iostreams.a and lib-isim-x86_64/libboost_iostreams.a have the same architectures (x86_64) and can't be in the same fat output file
make: *** [all] Error 1

Also I can't get the min ios version updated with MASON_PLATFORM_VERSION, it always stays at 8.0.

Here is my makefile

=============================
MASON_PLATFORM=ios
export MASON_PLATFORM
MASON_PLATFORM_VERSION=9.0
export MASON_PLATFORM_VERSION
MASON ?= .mason/mason

all:
#${MASON} install boost_libiostreams 1.63.0
${MASON} install geojson 0.4.0

============================

Start with the provided Makefile and the Mason install commands for boost_libiostreams and geojson. Inspect how the iOS architecture slices are produced and how MASON_PLATFORM_VERSION is handled, using the lipo errors as the initial failure case. Done means boost_libiostreams produces distinct expected slices and the requested minimum iOS version is honored.

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