thunderbird won't compiele whithout yasm installed Reproducible: Always
emerge --info and buildlog of failure is required reopen bug with appropriate information attached to bug report.
Created attachment 284407 [details] emerge --info
Created attachment 284409 [details] emerge thunderbird log i removed yasm first and then tried to compile thunderbird again
here is the info, you wonted
I can confirm this problem although the build stopped in some different places I resolved the problem the same way. Perhaps whatever it used when yasm wasn't present is unstable on 64 bit.
Created attachment 287479 [details] thunderbird build log
Created attachment 287483 [details] emerge --info
This happens for me as well. The build fails saying it needs yasm to build with webM.
This was added to Firefox, but somehow missed for Thunderbird. Fixed now, thanks for reporting!