iOS - Objective C dynamic framework emit bitcode for arch x86_64 (simulator)

Have setup a sample on Github, I'm using Xcode v 9.4.1 https://github.com/iousin/TreeFramework

Basically I'm trying to build my framework to include bitcode in the x86_64 simulator build. I tried various settings and tried building on command line, xcodebuild refuses to include bitcode in my simulator build, however it is very happy to include it in the arm64 (device) build.

All the following commands should be able to run from the same folder the above framework is checked out.

Following are the commands I've tried to build the above framework:

xcodebuild ENABLE_BITCODE[sdk=iphone*]=YES BITCODE_GENERATION_MODE=bitcode DYLIB_COMPATIBILITY_VERSION=1 -sdk iphonesimulator -configuration Release -target TreeFramework clean build 

xcodebuild OTHER_CFLAGS="-fembed-bitcode" ENABLE_BITCODE[sdk=iphone*]=YES BITCODE_GENERATION_MODE=bitcode -sdk iphonesimulator -configuration Release -target TreeFramework clean build 

xcodebuild OTHER_CFLAGS="-fembed-bitcode" ENABLE_BITCODE="YES" BITCODE_GENERATION_MODE="bitcode" -sdk iphonesimulator -configuration Release -target TreeFramework clean build

Ran the following to verify bitcode is emitted (it doesn't in this case).

otool -arch x86_64 -l build/Release-iphonesimulator/TreeFramework.framework/TreeFramework | grep LLVM

xcodebuild -sdk iphoneos -configuration Release -target TreeFramework clean build

    otool -arch arm64 -l build/Release-iphoneos/TreeFramework.framework/TreeFramework | grep LLVM

Appreciate any help.