Update scudo sanitizer runtime name

[etcwilde]

The Scudo sanitizer runtime name was changed from scudo-<arch>.{a,so} to scudo_standalone-<arch>.{a,so} in https://reviews.llvm.org/D138157.

@artemcm; I'm not sure how to deal with the fact that the driver may need to span across multiple toolchain versions here as there won't be a consistent runtime name that works for older and newer toolchains.

-- this is likely targeting the wrong branch, but I don't see a branch corresponding to rebranch on the driver.

This is part of the work for rebranch; rdar://114209408

[artemcm]

the fact that the driver may need to span across multiple toolchain versions here as there won't be a consistent runtime name

Perhaps this is something we could capture in the output of -print-target-info so that the compiler informs the driver.