[Support] Fix build for Haiku

[nielx]

Summary

This change fixes two issues with building LLVM on Haiku. The first issue is
that LLVM requires wait4(), which on Haiku is hidden behind the _BSD_SOURCE
feature flag when using the --std=c++14 flag. Additionally, the wait4()
function is only available in libbsd.so, so this is now a dependency.

The other fix is that Haiku does not have the (non-standard) rusage.maxrss
member, so by default the used memory info will be set to 0 on this platform.

[nielx]

Gentle reminder for the review request.

[nielx]

Adding reviewers from D82282 (another platform fix on this file)

[sepavloff]

This change looks good to me.

[nielx]

Thank you for the review. I cannot commit the change myself, so it would be much appreciated if somebody could land it for me.

Thanks!

[dexonsmith]

llvm/lib/Support/Unix/Program.inc

455–460

It's nice to minimize the #ifndef block when possible; I was able to simplify this slightly in 39ecfe614350fa5db7b8f13f81212f8e3831a390.

[sepavloff]

llvm/lib/Support/Unix/Program.inc

455–460

It's nice to minimize the #ifndef block when possible; I was able to simplify this slightly in 39ecfe614350fa5db7b8f13f81212f8e3831a390.

@dexonsmith Thank you!

llvm/lib/Support/CMakeLists.txt

elseif( CMAKE_HOST_UNIX )
   endif()
   set(system_libs ${system_libs} ${LLVM_PTHREAD_LIB})
   if( UNIX AND NOT (BEOS OR HAIKU) )
     set(system_libs ${system_libs} m)
   endif()
   if( FUCHSIA )
     set(system_libs ${system_libs} zircon)
   endif()
+  if ( HAIKU )
+    add_definitions(-D_BSD_SOURCE)
+    set(system_libs ${system_libs} bsd)
+  endif()
 endif( MSVC OR MINGW )
 
 # Delay load shell32.dll if possible to speed up process startup.
 set (delayload_flags)
 if (MSVC)
   set (delayload_flags delayimp -delayload:shell32.dll -delayload:ole32.dll)
 endif()
 

llvm/lib/Support/Unix/Program.inc

ProcessInfo llvm::sys::Wait(const ProcessInfo &PI, unsigned SecondsToWait,
   if (SecondsToWait && !WaitUntilTerminates) {
     alarm(0);
     sigaction(SIGALRM, &Old, nullptr);
   }
 
   if (ProcStat) {
     std::chrono::microseconds UserT = toDuration(Info.ru_utime);
     std::chrono::microseconds KernelT = toDuration(Info.ru_stime);
+#ifndef __HAIKU__
     uint64_t PeakMemory = static_cast<uint64_t>(Info.ru_maxrss);
     *ProcStat = ProcessStatistics{UserT + KernelT, UserT, PeakMemory};
+#else
+    *ProcStat = ProcessStatistics{UserT + KernelT, UserT, 0};
+#endif
   }
 
   // Return the proper exit status. Detect error conditions
   // so we can return -1 for them and set ErrMsg informatively.
   int result = 0;
   if (WIFEXITED(status)) {
     result = WEXITSTATUS(status);
     WaitResult.ReturnCode = result;