[llvm-profdata] Default to MemProf version 3

It's very confusing to have support for Verion 3 but not default to
it.  This patch teaches llvm-profdata to use MemProf version 3 by
default.

Author: kazutakahirata

llvm/tools/llvm-profdata/llvm-profdata.cpp

@@ -332,7 +332,7 @@ cl::opt<bool> DoWritePrevVersion(
 cl::opt<memprof::IndexedVersion> MemProfVersionRequested(
     "memprof-version", cl::Hidden, cl::sub(MergeSubcommand),
     cl::desc("Specify the version of the memprof format to use"),
-    cl::init(memprof::Version0),
+    cl::init(memprof::Version3),
     cl::values(clEnumValN(memprof::Version0, "0", "version 0"),
                clEnumValN(memprof::Version1, "1", "version 1"),
                clEnumValN(memprof::Version2, "2", "version 2"),