Don't use -1 as a value of an unsigned 7-bit enumeration; that has undefined

behavior and violates the !range constraints we put on loads of this enum.
Found by clang -fsanitize=enum.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170653 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DataLayout.h

@@ -39,6 +39,7 @@ class ArrayRef;
 
 /// Enum used to categorize the alignment types stored by LayoutAlignElem
 enum AlignTypeEnum {
+  INVALID_ALIGN = 0,                 ///< An invalid alignment
   INTEGER_ALIGN = 'i',               ///< Integer type alignment
   VECTOR_ALIGN = 'v',                ///< Vector type alignment
   FLOAT_ALIGN = 'f',                 ///< Floating point type alignment