Fixes a `std::set_difference` sorting violation in
`ASTReader::checkTargetOptions` that causes a crash when building clang
with `LLVM_ENABLE_EXPENSIVE_CHECKS` on libstdc++.
`accumulateFeaturesAsWritten` sorts target features using a custom
comparator that strips the `+`/`-` prefix (i.e. comparing `A.substr(1) <
B.substr(1)`). However, `std::set_difference` was being called with the
default `std::string::operator<` comparator, which does not match the
sorting order because `+` (ASCII 0x2B) is less than `-` (ASCII 0x2D).
For example, `["-cx16", "+sse2"]` is correctly sorted according to the
custom comparator, but incorrectly sorted according to the default
lexicographical comparator.
This patch fixes the issue by passing the same custom comparator used
for sorting to both `std::set_difference` calls.
Fixes#219046.
(cherry picked from commit dc222c2de55988f5359262a0e29fed5c14e824e7)
AZero13
0d261d1ca5