Kind of both? There were pre-standard compilers, but when they created the standard, they tried to make it so that one could write really dumb compilers and still fulfill the standard.
I suspect it was also the case that if they didn't make it easy for platform vendors to implement compilers then they wouldn't do it.
I suspect it was also the case that if they didn't make it easy for platform vendors to implement compilers then they wouldn't do it.