Allow lexer to handle string_view literals. Patch from Anton Bikineev.

This implements the compiler side of p0403r0. This patch was reviewed as
https://reviews.llvm.org/D26829.

llvm-svn: 290744
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 37c7aa4..6025a66 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -1713,9 +1713,9 @@
                                          getLangOpts());
         if (!isIdentifierBody(Next)) {
           // End of suffix. Check whether this is on the whitelist.
-          IsUDSuffix = (Chars == 1 && Buffer[0] == 's') ||
-                       NumericLiteralParser::isValidUDSuffix(
-                           getLangOpts(), StringRef(Buffer, Chars));
+          const StringRef CompleteSuffix(Buffer, Chars);
+          IsUDSuffix = StringLiteralParser::isValidUDSuffix(getLangOpts(),
+                                                            CompleteSuffix);
           break;
         }