[Support] Fix build for Haiku

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.

Reviewed By: sepavloff

Differential Revision: https://reviews.llvm.org/D87920

Patch by Niels Sascha Reedijk.

llvm/lib/Support/CMakeLists.txt

@@ -36,6 +36,10 @@ elseif( CMAKE_HOST_UNIX )
   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.

llvm/lib/Support/Unix/Program.inc

@@ -452,8 +452,12 @@ ProcessInfo llvm::sys::Wait(const ProcessInfo &PI, unsigned SecondsToWait,
   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