Some small changes in anticipation of an upcoming bigger change.
Should give a tiny boost to throughput and is (nearly) no diff.

Don't bother creating a new block for the GDV test, it can sit at
the end of the original block.

Bash the original ret expr instead of leaving it referring to a temp
local and/or nop.

-a alias supported by build.ps1

This data was previously held back because we weren't producing
builds with Linux or windows-x86 but now we are. The Linux builds
now produce only a single profdata file, coreclr.profdata, which 
should contain all the profile information for all the libraries in the
runtime.