ProfileData: Introduce InstrProfWriter using the naive text format

This isn't a format we'll want to write out in practice, but moving it
to the writer library simplifies llvm-profdata and isolates it from
further changes to the format.

This also allows us to update the tests to not rely on the text output
format.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204489 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ProfileData/InstrProf.h

@@ -31,7 +31,10 @@ struct instrprof_error {
     too_large,
     truncated,
     malformed,
-    unknown_function
+    unknown_function,
+    hash_mismatch,
+    count_mismatch,
+    counter_overflow
   };
   ErrorType V;