[llvm] RuntimeLibcalls: Add stub API for getting function signatures (PR #166290)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Hello, we see a test failure in our bot. It seems related to this PR. Could you please take a look? Thanks!
> 
> bot: https://lab.llvm.org/buildbot/#/builders/10/builds/16663
> 
> ```
> | Input was:
> # | <<<<<<
> # |             .
> # |             .
> # |             .
> # |           597: declare void @sincospi(...) 
> # |           598:  
> # |           599: declare void @sincospil(...) 
> # |           600:  
> # |           601: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: write, errnomem: write) 
> # |           602: declare void @__sincosf_stret(ptr sret({ float, float }) align 4, float) #0 
> # | check:17'0                                                                                X error: no match found
> # |           603:  
> # | check:17'0     ~
> # |           604: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: write, errnomem: write) 
> # | check:17'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> # |           605: declare void @__sincos_stret(ptr sret({ double, double }) align 8, double) #0 
> # | check:17'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> # | check:17'1     ?                                                                              possible intended match
> # |           606:  
> # | check:17'0     ~
> # |           607: declare void @sinhf(...) 
> # | check:17'0     ~~~~~~~~~~~~~~~~~~~~~~~~~
> # |           608:  
> # | check:17'0     ~
> # |           609: declare void @sinh(...) 
> # | check:17'0     ~~~~~~~~~~~~~~~~~~~~~~~~
> # |           610:  
> # | check:17'0     ~
> # |             .
> # |             .
> # |             .
> # | >>>>>>
> # `-----------------------------
> # error: command failed with exit status: 1
> ```

Should be fixed by e5f191e171720b413f83bff13b61d500369f560d

https://github.com/llvm/llvm-project/pull/166290