[clang] [clang] Fix a typo in clangs README (PR #114410)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/4425

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'lit :: shtest-external-shell-kill.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 23
env -u FILECHECK_OPTS "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.9/bin/python3.9" /Users/buildbot/buildbot-root/x86_64-darwin/llvm-project/llvm/utils/lit/lit.py -j1 --order=lexical -a Inputs/shtest-external-shell-kill | grep -v 'bash.exe: warning: could not find /tmp, please create!' | FileCheck /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/shtest-external-shell-kill.py
# executed command: env -u FILECHECK_OPTS /Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.9/bin/python3.9 /Users/buildbot/buildbot-root/x86_64-darwin/llvm-project/llvm/utils/lit/lit.py -j1 --order=lexical -a Inputs/shtest-external-shell-kill
# note: command had no output on stdout or stderr
# error: command failed with exit status: 1
# executed command: grep -v 'bash.exe: warning: could not find /tmp, please create!'
# executed command: FileCheck /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/shtest-external-shell-kill.py
# .---command stderr------------
# | /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/shtest-external-shell-kill.py:29:15: error: CHECK-NEXT: is not on the line after the previous match
# | # CHECK-NEXT: end
# |               ^
# | <stdin>:22:22: note: 'next' match was here
# | RUN: at line 5: echo end
# |                      ^
# | <stdin>:8:6: note: previous match ended here
# | start
# |      ^
# | <stdin>:9:1: note: non-matching line after previous match is here
# | 
# | ^
# | 
# | Input file: <stdin>
# | Check file: /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/shtest-external-shell-kill.py
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |          .
# |          .
# |          .
# |         17: RUN: at line 3: sleep 2 
# |         18: + sleep 2 
# |         19: + sleep 300 
# |         20: RUN: at line 4: kill $PID 
# |         21: + kill 69629 
# |         22: RUN: at line 5: echo end 
# | next:29                          !~~  error: match on wrong line
# |         23: /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/Inputs/shtest-external-shell-kill/Output/test.txt.script: line 5: echo: write error: Interrupted system call 
# |         24: /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/utils/lit/tests/Inputs/shtest-external-shell-kill/Output/test.txt.script: line 6: 69629 Terminated: 15 sleep 300 
# |         25:  
# |         26: -- 
# |         27:  
# |          .
# |          .
...

```

</details>

https://github.com/llvm/llvm-project/pull/114410