-fno-rtti incompatible with UBSAN fuzzing setup

[pitrou]

We have Apache Arrow set up on OSS-Fuzz. Arrow can optionally use Snappy to read Parquet files, but unfortunately Snappy cannot be enabled on some OSS-Fuzz builders because of incompatible compiler options.

See attempted CI run here:
https://github.com/google/oss-fuzz/actions/runs/10306444556/job/28529568675

and in particular these errors:

[1/5] Building CXX object CMakeFiles/snappy.dir/snappy-sinksource.cc.o
FAILED: CMakeFiles/snappy.dir/snappy-sinksource.cc.o 
/usr/local/bin/clang++ -DHAVE_CONFIG_H -I/work/snappy_ep-prefix/src/snappy_ep -O1 -fno-omit-frame-pointer -gline-tables-only -Wno-error=enum-constexpr-conversion -Wno-error=incompatible-function-pointer-types -Wno-error=int-conversion -Wno-error=deprecated-declarations -Wno-error=implicit-function-declaration -Wno-error=implicit-int -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=array-bounds,bool,builtin,enum,function,integer-divide-by-zero,null,object-size,return,returns-nonnull-attribute,shift,signed-integer-overflow,unsigned-integer-overflow,unreachable,vla-bound,vptr -fno-sanitize-recover=array-bounds,bool,builtin,enum,function,integer-divide-by-zero,null,object-size,return,returns-nonnull-attribute,shift,signed-integer-overflow,unreachable,vla-bound,vptr -fsanitize=fuzzer-no-link -stdlib=libc++ -Qunused-arguments -fcolor-diagnostics -fPIC -Wall -Wextra -Werror -fno-exceptions -fno-rtti -O2 -g -DNDEBUG -ggdb   -Wno-error -std=gnu++17 -MD -MT CMakeFiles/snappy.dir/snappy-sinksource.cc.o -MF CMakeFiles/snappy.dir/snappy-sinksource.cc.o.d -o CMakeFiles/snappy.dir/snappy-sinksource.cc.o -c /work/snappy_ep-prefix/src/snappy_ep/snappy-sinksource.cc
clang++: error: invalid argument '-fsanitize=vptr' not allowed with '-fno-rtti'

[etc.]

It would be nice if Snappy didn't force -fno-rtti unconditionally.

[kou]

It seems that this will not be accepted. See also: #147

[danilak-G]

I am ok with the idea of removing fno-rtti but I am afraid this is going to break ABI for quite a few users. Need to think and research how it affects ABI, maybe it's just for weird cases