[clang] [RISCV][FMV] Support target_version (PR #99040)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-hexagon-elf` running on `hexagon-build-02` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/40/builds/2132

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: CodeGen/attr-target-version-riscv-invalid.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: not /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/bin/clang -cc1 -internal-isystem /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/lib/clang/20/include -nostdsysteminc -triple riscv64 -target-feature +i -emit-llvm -o - /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c 2>&1 | /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/bin/FileCheck /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c --check-prefix=CHECK-UNSUPPORT-OS
+ /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/bin/FileCheck /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c --check-prefix=CHECK-UNSUPPORT-OS
+ not /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/bin/clang -cc1 -internal-isystem /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/stage1/lib/clang/20/include -nostdsysteminc -triple riscv64 -target-feature +i -emit-llvm -o - /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c
/local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c:3:24: error: CHECK-UNSUPPORT-OS: expected string not found in input
// CHECK-UNSUPPORT-OS: error: function multiversioning is currently only supported on Linux
                       ^
<stdin>:1:1: note: scanning from here
/local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c:8:48: error: function multiversioning doesn't support feature '<U+0000>'
^
<stdin>:1:128: note: possible intended match here
/local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c:8:48: error: function multiversioning doesn't support feature '<U+0000>'
                                                                                                                               ^

Input file: <stdin>
Check file: /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           1: /local/mnt/workspace/bots/hexagon-build-02/clang-hexagon-elf/llvm/clang/test/CodeGen/attr-target-version-riscv-invalid.c:8:48: error: function multiversioning doesn't support feature '<U+0000>' 
check:3'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
check:3'1                                                                                                                                    ?                                                                   possible intended match
           2:  8 | __attribute__((target_version("arch=+c"))) int foo(void) { 
check:3'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           3:  | ^ 
check:3'0     ~~~~~
           4: 1 error generated. 
check:3'0     ~~~~~~~~~~~~~~~~~~~
>>>>>>

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/99040