Donald Knuth said "The Itanium approach...was supposed to be so terrific—until it turned out that the wished-for compilers were basically impossible to write."[82]

https://en.wikipedia.org/wiki/Itanic

So they didn't have the needed compiler

Surely there were compilers, they just weren't as good (as optimizing) as Intel wished.

Of course there were itanic-targetting compilers, they worked, just not well enough to deliver on marketing promise (edit: and what the hardware was theoretically capable of).

I wonder how HP and Microsoft managed to port HP-UX and Windows without a compiler.

That's kind of the point.

Compilers existed just fine to do the porting, and solved that problem.

Intel's failure is that they were unable to solve a different problem because that compiler didn't exist, one that went well beyond merely porting.

In other words, "That's what compilers are for." is a perfectly fine attitude when those compilers exist, and a bad attitude when they don't exist. Porting is the former, making VLIW efficient is the latter.