testsuite: fix dwarf2/utf-1.C with DWARF4

Running
$ make check-c++ RUNTESTFLAGS='--target_board=unix\{-gdwarf-5,-gdwarf-4\} dwarf2.exp=utf-1.C'
shows
FAIL: g++.dg/debug/dwarf2/utf-1.C  -std=gnu++20  scan-assembler-times DW_AT_encoding \\(0x10\\) 3
because with -gdwarf-4 the output is:

  .byte   0x10    # DW_AT_encoding

but with -gdwarf-5 the output is the expected:

                # DW_AT_encoding (0x10)

The difference is caused by the DWARF5 optimize_implicit_const
optimization:
<https://gcc.gnu.org/pipermail/gcc-patches/2016-October/459762.html>

I suppose we could do what testsuite/rust/debug/chartype.rs does
and just run the test with -gdwarf-4.

gcc/testsuite/ChangeLog:

	* g++.dg/debug/dwarf2/utf-1.C: Use -gdwarf-4.  Adjust expected
	output.

1 files changed, 7 insertions, 2 deletions

diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/utf-1.C b/gcc/testsuite/g++.dg/debug/dwarf2/utf-1.C
index 43b354f..0ce4d87 100644
--- a/gcc/testsuite/g++.dg/debug/dwarf2/utf-1.C
+++ b/gcc/testsuite/g++.dg/debug/dwarf2/utf-1.C
@@ -1,8 +1,13 @@
 // { dg-do compile { target c++20 } }
-// { dg-options { -gdwarf -dA } }
+// { dg-options { -gdwarf-4 -dA } }
 
 // Test that all three use DW_ATE_UTF.
-// { dg-final { scan-assembler-times {DW_AT_encoding \(0x10\)} 3 } }
+// This test uses -gdwarf-4 since in DWARF5 optimize_implicit_const
+// would optimize the output from:
+//   .byte   0x10    # DW_AT_encoding
+// into:
+//                   # DW_AT_encoding (0x10)
+// { dg-final { scan-assembler-times "0x10\[ \t]\[^\n\r]* DW_AT_encoding" 3 } }
 
 char8_t c8;
 char16_t c16;