[llvm] [CAS] Add llvm-cas tools to inspect on-disk LLVMCAS (PR #166481)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64-flang-aix` running on `ppc64-flang-aix-test` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/201/builds/7000

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (build-unified-tree) failure: build (failure)
...
ld: 0711-415 WARNING: Symbol _ZN4llvm15MCTargetOptionsaSEOS0_ is already exported.
ld: 0711-415 WARNING: Symbol _ZN4llvm17DiagnosticHandlerD2Ev is already exported.
ld: 0711-415 WARNING: Symbol _ZN4llvm24StandardInstrumentationsD2Ev is already exported.
ld: 0711-415 WARNING: Symbol _ZN4llvm28PassInstrumentationCallbacksD2Ev is already exported.
ld: 0711-415 WARNING: Symbol _ZN4llvm2cl3optINSt3__112basic_stringIcNS2_11char_traitsIcEENS2_9allocatorIcEEEELb0ENS0_6parserIS8_EEEC2IJA17_cNS0_12OptionHiddenENS0_4descEEEEDpRKT_ is already exported.
ld: 0711-415 WARNING: Symbol _ZTVN4llvm2cl11OptionValueIcEE is already exported.
9544.664 [66/2/8410] Linking CXX executable bin/lli-child-target
9545.088 [65/2/8411] Linking CXX executable bin/llvm-bcanalyzer
9545.131 [64/2/8412] Linking CXX executable bin/llvm-as
9545.404 [63/2/8413] Linking CXX executable bin/llvm-cas
FAILED: [code=8] bin/llvm-cas 
: && /home/llvm/llvm-external-buildbots/clang.20.1.7/bin/clang++ -mcmodel=large -fPIC -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -Wl,-bnoipath -Wl,-bglink=large tools/llvm-cas/CMakeFiles/llvm-cas.dir/llvm-cas.cpp.o -o bin/llvm-cas  -Wl,-blibpath:"\$ORIGIN/../lib:/usr/lib:/lib"  lib/libLLVMSupport.a  lib/libLLVMCAS.a  lib/libLLVMOption.a  -lrt  -lld  -lpthreads  -lm  lib/libLLVMDemangle.a && :
ld: 0711-317 ERROR: Undefined symbol: .flock
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.
clang++: error: linker command failed with exit code 8 (use -v to see invocation)
9549.628 [63/1/8414] Linking CXX executable bin/llvm-c-test
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/166481