Add zig_llvm-ar.cpp in build.zig

This was added in 0afb5b2ec6de494efe0605b2270f6a01b95237af 8 days ago, but it seems it was only added in the cmake files and not build.zig
c8ee445c86Nicolas committed on 6/6/2021, 2:54:33 AM· committed by Andrew Kelleyparent072c320
1 file changedLine totals unavailable