[clang] [HLSL] Enable -fconvergent-functions by default (PR #86571)

[via cfe-commits]

aniplcc wrote:

check fails with
```
/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/clang/test/CodeGenHLSL/convergent-functions.hlsl:7:11: error: CHECK: expected string not found in input
// CHECK: define void {{.*}}fn{{.*}}()
          ^
<stdin>:1:1: note: scanning from here
; ModuleID = '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/clang/test/CodeGenHLSL/convergent-functions.hlsl'
^
<stdin>:7:10: note: possible intended match here
define spir_func void @_Z2fnv() #0 {
         ^
Input file: <stdin>
Check file: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/clang/test/CodeGenHLSL/convergent-functions.hlsl
-dump-input=help explains the following input dump.
Input was:
<<<<<<
           1: ; ModuleID = '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/clang/test/CodeGenHLSL/convergent-functions.hlsl'
check:7'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           2: source_filename = "/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-6mhbj-1/llvm-project/github-pull-requests/clang/test/CodeGenHLSL/convergent-functions.hlsl"
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           3: target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           4: target triple = "spirv-linux-vulkan-library"
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           5:
check:7'0     ~
           6: ; Function Attrs: convergent noinline nounwind optnone
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           7: define spir_func void @_Z2fnv() #0 {
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:7'1              ?                            possible intended match
           8: entry:
check:7'0     ~~~~~~~
           9:  ret void
check:7'0     ~~~~~~~~~~
          10: }
check:7'0     ~~
          11:
check:7'0     ~
          12: attributes #0 = { convergent noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
check:7'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           .
           .
           .
>>>>>>
--

```

https://github.com/llvm/llvm-project/pull/86571