Remove exception handling usage from tblgen.

Most places can use PrintFatalError as the unwinding mechanism was not
used for anything other than printing the error. The single exception
was CodeGenDAGPatterns.cpp, where intermediate errors during type
resolution were ignored to simplify incremental platform development.
This use is replaced by an error flag in TreePattern and bailout earlier
in various places if it is set. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166712 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/CodeGenTarget.h b/utils/TableGen/CodeGenTarget.h
index 672b140..ddeecee 100644
--- a/utils/TableGen/CodeGenTarget.h
+++ b/utils/TableGen/CodeGenTarget.h
@@ -9,8 +9,8 @@
 //
 // This file defines wrappers for the Target class and related global
 // functionality.  This makes it easier to access the data and provides a single
-// place that needs to check it for validity.  All of these classes throw
-// exceptions on error conditions.
+// place that needs to check it for validity.  All of these classes abort
+// on error conditions.
 //
 //===----------------------------------------------------------------------===//