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.
053876cdbe