[yaml2obj][MachO] Don't fill dummy data for virtual sections
Currently, MachOWriter::writeSectionData writes dummy data (0xdeadbeef) to fill section data areas in the file even if the section is a virtual one. Since virtual sections don't occupy any space in the file, writing dummy data could results the "OS.tell() - fileStart <= Sec.offset" assertion failure.
This patch fixes the bug by simply not writing any dummy data for virtual sections.
Reviewers: beanz, jhenderson, rupprecht, alexshap
Reviewed By: alexshap
Subscribers: compnerd, llvm-commits
Differential Revision: https://reviews.llvm.org/D62991