`Linux/instrprof-vtable-value-prof.cpp` needs to be built for the test
to run. However, cpp compile & link failed with undefined-ABI error [1].
See original failure in
https://lab.llvm.org/buildbot/#/builders/18/builds/16429
[1]
```
FAIL: Profile-powerpc64 :: Linux/instrprof-vtable-value-prof.cpp (2406 of 2414)
******************** TEST 'Profile-powerpc64 :: Linux/instrprof-vtable-value-prof.cpp' FAILED ********************
Exit Code: 1
Command Output (stderr):
--
RUN: at line 3: /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/build_debug/./bin/clang --driver-mode=g++ -m64 -ldl -fprofile-generate -fuse-ld=lld -O2 -g -fprofile-generate=. -mllvm -enable-vtable-value-profiling /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/llvm-project/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp -o /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/build_debug/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc64/Linux/Output/instrprof-vtable-value-prof.cpp.tmp-test
+ /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/build_debug/./bin/clang --driver-mode=g++ -m64 -ldl -fprofile-generate -fuse-ld=lld -O2 -g -fprofile-generate=. -mllvm -enable-vtable-value-profiling /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/llvm-project/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp -o /home/buildbots/llvm-external-buildbots/workers/ppc64be-sanitizer/sanitizer-ppc64be/build/build_debug/runtimes/runtimes-bins/compiler-rt/test/profile/Profile-powerpc64/Linux/Output/instrprof-vtable-value-prof.cpp.tmp-test
ld.lld: error: /lib/../lib64/Scrt1.o: ABI version 1 is not supported
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```
(The profile format change is split into a standalone change into https://github.com/llvm/llvm-project/pull/81691)
* For InstrFDO value profiling, implement instrumentation and lowering for virtual table address.
* This is controlled by `-enable-vtable-value-profiling` and off by default.
* When the option is on, raw profiles will carry serialized `VTableProfData` structs and compressed vtables as payloads.
* Implement profile reader and writer support
* Raw profile reader is used by `llvm-profdata` but not compiler. Raw profile reader will construct InstrProfSymtab with symbol names, and map profiled runtime address to vtable symbols.
* Indexed profile reader is used by `llvm-profdata` and compiler. When initialized, the reader stores a pointer to the beginning of in-memory compressed vtable names and the length of string. When used in `llvm-profdata`, reader decompress the string to show symbols of a profiled site. When used in compiler, string decompression doesn't
happen since IR is used to construct InstrProfSymtab.
* Indexed profile writer collects the list of vtable names, and stores that to index profiles.
* Text profile reader and writer support are added but mostly follow the implementation for indirect-call value type.
* `llvm-profdata show -show-vtables <args> <profile>` is implemented.
rfc in
https://discourse.llvm.org/t/rfc-dynamic-type-profiling-and-optimizations-in-llvm/74600#pick-instrumentation-points-and-instrument-runtime-types-7
