This is done by detecting the 40 character git sha in the SDK version
and creating a new set of tools based on this SHA. This works for any
command that uses expand_sdk_name (i.e. install activate and update) but
it wont show up in the output of `list`.
For example:
./emsdk install sdk-releases-upstream-b0cfdb236483b6828ee2e3f263fd94f011ed1863-64bit
Or just:
./emsdk install releases-upstream-b0cfdb236483b6828ee2e3f263fd94f011ed1863