preprocessor/106426: Treat u8 character literals as unsigned in char8_t modes.

This patch corrects handling of UTF-8 character literals in preprocessing
directives so that they are treated as unsigned types in char8_t enabled
C++ modes (C++17 with -fchar8_t or C++20 without -fno-char8_t). Previously,
UTF-8 character literals were always treated as having the same type as
ordinary character literals (signed or unsigned dependent on target or use
of the -fsigned-char or -funsigned char options).

	PR preprocessor/106426

gcc/c-family/ChangeLog:
	* c-opts.cc (c_common_post_options): Assign cpp_opts->unsigned_utf8char
	subject to -fchar8_t, -fsigned-char, and/or -funsigned-char.

gcc/testsuite/ChangeLog:
	* g++.dg/ext/char8_t-char-literal-1.C: Check signedness of u8 literals.
	* g++.dg/ext/char8_t-char-literal-2.C: Check signedness of u8 literals.

libcpp/ChangeLog:
	* charset.cc (narrow_str_to_charconst): Set signedness of CPP_UTF8CHAR
	literals based on unsigned_utf8char.
	* include/cpplib.h (cpp_options): Add unsigned_utf8char.
	* init.cc (cpp_create_reader): Initialize unsigned_utf8char.

1 files changed, 2 insertions, 2 deletions

diff --git a/libcpp/charset.cc b/libcpp/charset.cc
index ca8b7cf..12e3163 100644
--- a/libcpp/charset.cc
+++ b/libcpp/charset.cc
@@ -1960,8 +1960,8 @@ narrow_str_to_charconst (cpp_reader *pfile, cpp_string str,
   /* Multichar constants are of type int and therefore signed.  */
   if (i > 1)
     unsigned_p = 0;
-  else if (type == CPP_UTF8CHAR && !CPP_OPTION (pfile, cplusplus))
-    unsigned_p = 1;
+  else if (type == CPP_UTF8CHAR)
+    unsigned_p = CPP_OPTION (pfile, unsigned_utf8char);
   else
     unsigned_p = CPP_OPTION (pfile, unsigned_char);