[clang] [clang] Add [[clang::returns_argument]] (PR #169815)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 84776 tests passed
* 1119 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang
<details>
<summary>Clang.Misc/pragma-attribute-supported-attributes-list.test</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang-tblgen -gen-clang-test-pragma-attribute-supported-attributes -I/home/gha/actions-runner/_work/llvm-project/llvm-project/clang/include /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/include/clang/Basic/Attr.td -o - | /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Misc/pragma-attribute-supported-attributes-list.test
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang-tblgen -gen-clang-test-pragma-attribute-supported-attributes -I/home/gha/actions-runner/_work/llvm-project/llvm-project/clang/include /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/include/clang/Basic/Attr.td -o -
# note: command had no output on stdout or stderr
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Misc/pragma-attribute-supported-attributes-list.test
# .---command stderr------------
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Misc/pragma-attribute-supported-attributes-list.test:188:16: error: CHECK-NEXT: is not on the line after the previous match
# | // CHECK-NEXT: ReturnsNonNull (SubjectMatchRule_objc_method, SubjectMatchRule_function)
# |                ^
# | <stdin>:185:1: note: 'next' match was here
# | ReturnsNonNull (SubjectMatchRule_objc_method, SubjectMatchRule_function)
# | ^
# | <stdin>:183:84: note: previous match ended here
# | ReturnTypestate (SubjectMatchRule_function, SubjectMatchRule_variable_is_parameter)
# |                                                                                    ^
# | <stdin>:184:1: note: non-matching line after previous match is here
# | ReturnsArgument (SubjectMatchRule_function)
# | ^
# | 
# | Input file: <stdin>
# | Check file: /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Misc/pragma-attribute-supported-attributes-list.test
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |           .
# |           .
# |           .
# |         180: ReleaseHandle (SubjectMatchRule_variable_is_parameter) 
# |         181: ReqdWorkGroupSize (SubjectMatchRule_function) 
# |         182: Restrict (SubjectMatchRule_function) 
# |         183: ReturnTypestate (SubjectMatchRule_function, SubjectMatchRule_variable_is_parameter) 
# |         184: ReturnsArgument (SubjectMatchRule_function) 
# |         185: ReturnsNonNull (SubjectMatchRule_objc_method, SubjectMatchRule_function) 
# | next:188     !~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  error: match on wrong line
# |         186: ReturnsTwice (SubjectMatchRule_function) 
# |         187: SYCLExternal (SubjectMatchRule_function) 
# |         188: SYCLKernelEntryPoint (SubjectMatchRule_function) 
# |         189: SYCLSpecialClass (SubjectMatchRule_record) 
# |         190: ScopedLockable (SubjectMatchRule_record) 
# |           .
# |           .
# |           .
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/169815