`libCYaml.a` has wrong arch on M1 Mac about swift-driver HOT 1 CLOSED

So, the best fix I found so far is to force libCYaml.a to be built as a fat binary with both arm64 and x86_64 inside the Yams repo by adding
set(CMAKE_OSX_ARCHITECTURES "arm64;x86_64")
at the top of Sources/CYaml/CMakeLists.txt.

Without it generated build.ninja for CYaml sources will contain -arch arm64 flag and results in a arm64 binary when x86_64 is expected, even though we explicitly pass -DCMAKE_C_FLAGS=-target arm64-apple-macosx10.15 to cmake.🤔

This is a workaround unblockes me on building the swift toolchain on M1, but we need a better fix somewhere in build-script-helper.py, because current CMAKE_C_FLAGS it passes isn't enough to convince cmake to generate right flags for libCYaml.a. I am no expert in cmake, so idk how to do this.

@edymtt Can you take a look at this problem, it currently blocks toolchain build on M1 macs.

It is probably one line fix here, but I cannot add CMAKE_OSX_ARCHITECTURES since Yams has Swift sources as well and cmake doesn't allow using it.

from swift-driver.