[clang] [CIR] Add bit ffs operation (PR #150997)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-x86_64-debian` running on `lldb-x86_64-debian` while building `clang` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/27802

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

```
Step 6 (test) failure: build (failure)
...
PASS: lldb-api :: functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py (34 of 3101)
PASS: lldb-api :: functionalities/gdb_remote_client/TestRegDefinitionInParts.py (35 of 3101)
PASS: lldb-api :: python_api/watchpoint/watchlocation/TestSetWatchlocation.py (36 of 3101)
PASS: lldb-api :: commands/watchpoints/hello_watchlocation/TestWatchLocation.py (37 of 3101)
PASS: lldb-api :: functionalities/thread/main_thread_exit/TestMainThreadExit.py (38 of 3101)
PASS: lldb-api :: tools/lldb-server/TestGdbRemoteForkResume.py (39 of 3101)
PASS: lldb-api :: tools/lldb-server/TestGdbRemote_vCont.py (40 of 3101)
PASS: lldb-api :: functionalities/data-formatter/data-formatter-stl/generic/bitset/TestDataFormatterGenericBitset.py (41 of 3101)
PASS: lldb-api :: tools/lldb-dap/runInTerminal/TestDAP_runInTerminal.py (42 of 3101)
UNRESOLVED: lldb-api :: tools/lldb-dap/variables/TestDAP_variables.py (43 of 3101)
******************** TEST 'lldb-api :: tools/lldb-dap/variables/TestDAP_variables.py' FAILED ********************
Script:
--
/usr/bin/python3 /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./lib --env LLVM_INCLUDE_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/include --env LLVM_TOOLS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./bin --arch x86_64 --build-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex --lldb-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/lldb --compiler /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/clang --dsymutil /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./bin --lldb-obj-root /home/worker/2.0.1/lldb-x86_64-debian/build/tools/lldb --lldb-libs-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./lib --cmake-build-type Release -t /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/tools/lldb-dap/variables -p TestDAP_variables.py
--
Exit Code: 1

Command Output (stdout):
--
lldb version 22.0.0git (https://github.com/llvm/llvm-project.git revision 1249ab9a0364805c84dc57b57fc4e85c1c7d5d69)
  clang revision 1249ab9a0364805c84dc57b57fc4e85c1c7d5d69
  llvm revision 1249ab9a0364805c84dc57b57fc4e85c1c7d5d69
Skipping the following test categories: ['libc++', 'msvcstl', 'dsym', 'gmodules', 'debugserver', 'objc']

--
Command Output (stderr):
--
Change dir to: /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/tools/lldb-dap/variables
UNSUPPORTED: LLDB (/home/worker/2.0.1/lldb-x86_64-debian/build/bin/clang-x86_64) :: test_darwin_dwarf_missing_obj (TestDAP_variables.TestDAP_variables.test_darwin_dwarf_missing_obj) (requires one of macosx, darwin, ios, tvos, watchos, bridgeos, iphonesimulator, watchsimulator, appletvsimulator) 
UNSUPPORTED: LLDB (/home/worker/2.0.1/lldb-x86_64-debian/build/bin/clang-x86_64) :: test_darwin_dwarf_missing_obj_with_symbol_ondemand_enabled (TestDAP_variables.TestDAP_variables.test_darwin_dwarf_missing_obj_with_symbol_ondemand_enabled) (requires one of macosx, darwin, ios, tvos, watchos, bridgeos, iphonesimulator, watchsimulator, appletvsimulator) 
runCmd: settings clear --all

output: 

runCmd: settings set symbols.enable-external-lookup false

output: 

runCmd: settings set target.inherit-tcc true

output: 

runCmd: settings set target.disable-aslr false

output: 

runCmd: settings set target.detach-on-error false

output: 

```

</details>

https://github.com/llvm/llvm-project/pull/150997