This patch adds YAML read/write support to llvm-profdata. The primary
intent is to accommodate MemProf profiles in test cases, thereby
avoiding the binary format.
The read support is via llvm-profdata merge. This is useful when we
want to verify that the compiler does the right thing on a given .ll
file and a MemProf profile in a test case. In the test case, we would
convert the MemProf profile in YAML to an indexed profile and invoke
the compiler on the .ll file along with the indexed profile.
The write support is via llvm-profdata show --memory. This is useful
when we wish to convert an indexed MemProf profile to YAML while
writing tests. We would compile a test case in C++, run it for an
indexed MemProf profile, and then convert it to the text format.
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