Ray
I got that message as well.
I tracked it down to gcc not being able to find libiconv-2.dll but I presumed that I'd managed to break the files somehow by trying to move the hardware files out of that installation
But I did a rebooot and unzipped again at about 10pm last night and it still didn't work, so I gave up for the day.
I could have sworn that initially when I unzipped the package it worked ok, but it was getting late by the time I started looking at it, so I could have been mistaken.
But perhaps the download zip files are indeed broken.
I didn't try compiling for AVR, which I think I should have done
It will be easier to get working in the correct location e.g. The hardware folder if it is indeed a problem with that copy of the IDE
Ray.
I just took a look again, and it does compile for the UNO with that file set, just not for xtensia
So they seem to have stuffed up the compiler installation
If you want to just check whether your board could work with the arduino IDE you could download my version, because at least it compiles
However in the longer term the one from ESP8266 Community Forum ยท GitHub is undoubtedly better in many ways
I'm going to see if I can fix the compiler issue by using the compiler from my version, and just as a matter of interest I will try installing on an old Windows XP machine I keep for regression testing.
Edit.
After a lot of messing around I can get the better version to compile, but it now worn't run the uploader 
So unless you are desperate to play with the ESP8266 this weekend, you'd probably be better off doing something that doesnt require your to tear your hair out 
And I'll wait for the author of the repo to fix whatever is wrong. (I've posted a couple of issues to github)