Our YAML library's handling of tags isn't perfect, but it is good enough to get rid of the need for the --format argument to yaml2obj. This patch does exactly that.
Instead of requiring --format, it infers the format based on the tags found in the object file. The supported tags are:
!ELF
!COFF
!mach-o
!fat-mach-o
I have a corresponding patch that is quite large that fixes up all the in-tree test cases.