Taken from ports LLVM.
Need -lexecinfo for Backtrace symbols.

Index: driver/linker-gcc.cpp
--- driver/linker-gcc.cpp.orig
+++ driver/linker-gcc.cpp
@@ -414,7 +414,6 @@ void ArgsBuilder::addCppStdlibLinkFlags(const llvm::Tr
     break;
   case llvm::Triple::Solaris:
   case llvm::Triple::NetBSD:
-  case llvm::Triple::OpenBSD:
   case llvm::Triple::DragonFly:
     args.push_back("-lstdc++");
     break;
@@ -424,6 +423,7 @@ void ArgsBuilder::addCppStdlibLinkFlags(const llvm::Tr
   case llvm::Triple::WatchOS:
   case llvm::Triple::TvOS:
   case llvm::Triple::FreeBSD:
+  case llvm::Triple::OpenBSD:
     args.push_back("-lc++");
     break;
   default:
@@ -665,11 +665,14 @@ void ArgsBuilder::addDefaultPlatformLibs() {
     args.push_back("-lrt");
     args.push_back("-ldl");
   // fallthrough
+  case llvm::Triple::OpenBSD:
+    args.push_back("-lexecinfo");
+    args.push_back("-lc++abi");
+  // fallthrough
   case llvm::Triple::Darwin:
   case llvm::Triple::MacOSX:
   case llvm::Triple::FreeBSD:
   case llvm::Triple::NetBSD:
-  case llvm::Triple::OpenBSD:
   case llvm::Triple::DragonFly:
     addSoname = true;
     args.push_back("-lpthread");