[gcc r12-6716] c++: fix PR104025 change

[Jason Merrill]

https://gcc.gnu.org/g:bd0ef3534816a1b8ffad544d9ed720690a97d7cc

commit r12-6716-gbd0ef3534816a1b8ffad544d9ed720690a97d7cc
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Jan 18 22:11:56 2022 -0500

    c++: fix PR104025 change
    
    Somehow I pushed my earlier patch without it actually fixing the test; we
    need input_location to be for the last consumed token, not the next one.
    
    gcc/cp/ChangeLog:
    
            * parser.cc (saved_token_sentinel::rollback): Use
            cp_lexer_previous_token.

Diff:
---
 gcc/cp/parser.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 60d9f7bb723..00279c43404 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -1308,7 +1308,8 @@ struct saved_token_sentinel
   void rollback ()
   {
     cp_lexer_rollback_tokens (lexer);
-    cp_lexer_set_source_position (lexer);
+    cp_lexer_set_source_position_from_token
+      (cp_lexer_previous_token (lexer));
     mode = STS_DONOTHING;
   }
   ~saved_token_sentinel ()