[PATCH] [gdb/build] Fix cli/cli-style.c build error with C++20

PR build/34514 reports for a C++20 build:
...
cli/cli-style.c:457:37: error: conversion from ‘const char8_t [8]’ to \
  non-scalar type ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} \
  requested
  457 | static std::string warning_prefix = u8"\u26A0\uFE0F ";
      |                                     ^~~~~~~~~~~~~~~~~
...

The u8 literal is char[] until C++20, but char8_t[] since C++20.

Fix this by using a reinterpret_cast<const char *>.

Tested by rebuilding using GCC 15.3.0, with and without -std=c++20.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34514
---
 gdb/cli/cli-style.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/gdb/cli/cli-style.c b/gdb/cli/cli-style.c
index 60c00acdf43..5c26519c6d7 100644
--- a/gdb/cli/cli-style.c
+++ b/gdb/cli/cli-style.c
@@ -454,7 +454,8 @@ no_emojis ()
    - uFE0F: Variation Selector-16 (VS16)
    The VS16 forces "Emoji" presentation.  It is needed because the default
    presentation for Warning Sign is "Text".  Together, we get: ⚠️ .  */
-static std::string warning_prefix = u8"\u26A0\uFE0F ";
+static std::string warning_prefix
+  = reinterpret_cast<const char *> (u8"\u26A0\uFE0F ");
 
 /* Implement 'show style warning-prefix'.  */
 
@@ -479,7 +480,8 @@ print_warning_prefix (ui_file *file)
    - u274C: Cross Mark: ❌
    No VS16 is needed because the default presentation for Cross Mark is
    "Emoji".  */
-static std::string error_prefix = u8"\u274C ";
+static std::string error_prefix
+  = reinterpret_cast<const char *> (u8"\u274C ");
 
 /* Implement 'show style error-prefix'.  */
 

base-commit: dbf19e0f878eb592011c25c1dbbfc35eee330ec2
-- 
2.51.0