[llvm] [llvm-profdata] Enabled functionality to write split-layout profile (PR #101795)

[William Junda Huang via llvm-commits]

huangjd wrote:

> Update change summary: split_layout -> split-layout
> 
> > but previously there is no way to use it from llvm-profdata.
> 
> How was it previously used?

There is a function in SampleProfileWriter `resetSecLayout` which can be called with the value CtxSplitLayout to change it into split layout. It is not used anywhere in LLVM so there is no user access to it. However in our internal tools we do call this function to create such profile. This patch make this option available to the user. 

https://github.com/llvm/llvm-project/pull/101795