\brief Return the offset of the field represented by the Cursor.
If the cursor is not a field declaration, -1 is returned.
If the cursor semantic parent is not a record field declaration,
CXTypeLayoutError_Invalid is returned.
If the field's type declaration is an incomplete type,
CXTypeLayoutError_Incomplete is returned.
If the field's type declaration is a dependent type,
CXTypeLayoutError_Dependent is returned.
If the field's name S is not found,
CXTypeLayoutError_InvalidFieldName is returned.
\brief Return the offset of the field represented by the Cursor.
If the cursor is not a field declaration, -1 is returned. If the cursor semantic parent is not a record field declaration, CXTypeLayoutError_Invalid is returned. If the field's type declaration is an incomplete type, CXTypeLayoutError_Incomplete is returned. If the field's type declaration is a dependent type, CXTypeLayoutError_Dependent is returned. If the field's name S is not found, CXTypeLayoutError_InvalidFieldName is returned.