InstrProf: Give coverage its own errors instead of piggy backing on instrprof

Since the coverage mapping reader and the instrprof reader were
emitting a shared set of error codes, the error messages you'd get
back from llvm-cov were ambiguous about what was actually wrong. Add
another error category to fix this.

I've also improved the wording on a couple of the instrprof errors,
for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236665 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ProfileData/CoverageMapping.h

@@ -484,7 +484,26 @@ template<> struct DenseMapInfo<coverage::CounterExpression> {
   }
 };
 
+const std::error_category &coveragemap_category();
+
+enum class coveragemap_error {
+  success = 0,
+  eof,
+  no_data_found,
+  unsupported_version,
+  truncated,
+  malformed
+};
+
+inline std::error_code make_error_code(coveragemap_error E) {
+  return std::error_code(static_cast<int>(E), coveragemap_category());
+}
 
 } // end namespace llvm
 
+namespace std {
+template <>
+struct is_error_code_enum<llvm::coveragemap_error> : std::true_type {};
+}
+
 #endif // LLVM_PROFILEDATA_COVERAGEMAPPING_H_