Fixes issue with linking lib_unwind on OpenBSD

[wmoxam]

Fixes #5280

I'm not sure but I think the problem may be related to OpenBSD's change of default compiler to Clang, and the update of LLVM to v5 in ports.

[RX14]

Are we sure that libunwind doesn't exist as a seperate library to libstdc++?

[wmoxam]

Yes

[ysbaddaden]

Yes, switching from GCC to clang by default is probably the reason it broke.

I guess if you switch to GCC it links libgcc or something approaching. I'm not sure we have to link libstdc++. Maybe rely on libunwind?

[ysbaddaden]

Looking at a binary linked on OpenBSD 6.0, I notice it linked to libestdc++. I don't know how it relates to libstdc++ thought.

[valpackett]

On FreeBSD 12 (LLVM 5.0 in base), Crystal links to libc++, no libunwind:

/usr/local/bin/crystal:
        librt.so.1 => /usr/lib/librt.so.1 (0x802d83000)
        libncurses.so.8 => /lib/libncurses.so.8 (0x802f88000)
        libthr.so.3 => /lib/libthr.so.3 (0x8031dd000)
        libz.so.6 => /lib/libz.so.6 (0x803404000)
        libm.so.5 => /lib/libm.so.5 (0x80361d000)
        libc++.so.1 => /usr/lib/libc++.so.1 (0x80384a000)
        libcxxrt.so.1 => /lib/libcxxrt.so.1 (0x803b16000)
        libpcre.so.1 => /usr/local/lib/libpcre.so.1 (0x803d34000)
        libgc-threaded.so.1 => /usr/local/lib/libgc-threaded.so.1 (0x803fab000)
        libevent-2.1.so.6 => /usr/local/lib/libevent-2.1.so.6 (0x804203000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x804452000)
        libc.so.7 => /lib/libc.so.7 (0x804668000)
        libcrypto.so.8 => /lib/libcrypto.so.8 (0x804e00000)

Did OpenBSD keep libstdc++ as the default C++ lib when switching to LLVM/clang?

[wmoxam]

$ uname -sr 
OpenBSD 6.2
$ nm -D  /usr/lib/libc++.so.1.0 | grep Unwind
         U _Unwind_Resume
$ nm -D  /usr/lib/libstdc++.so.57.0  | grep Unwind                                                                                     
00080480 T _Unwind_Backtrace
0007eb10 T _Unwind_DeleteException
0007edc0 T _Unwind_FindEnclosingFunction
000824f0 T _Unwind_Find_FDE
00080920 T _Unwind_ForcedUnwind
0007eaa0 T _Unwind_GetCFA
0007eaf0 T _Unwind_GetDataRelBase
0007eb80 T _Unwind_GetGR
0007eab0 T _Unwind_GetIP
0007edf0 T _Unwind_GetIPInfo
0007ead0 T _Unwind_GetLanguageSpecificData
0007eae0 T _Unwind_GetRegionStart
0007eb00 T _Unwind_GetTextRelBase
00080a40 T _Unwind_RaiseException
00080820 T _Unwind_Resume
00080bd0 T _Unwind_Resume_or_Rethrow
0007eb30 T _Unwind_SetGR
0007eac0 T _Unwind_SetIP

[ysbaddaden]

I booted an OpenBSD 6.2 box and found out that Unwind symbols are in libc++abi instead of libc++. See http://libcxxabi.llvm.org/spec.html

Maybe we can just link c++abi instead of the whole stdc++?

[RX14]

Presuming you've tested this, this is fine.

[wmoxam]

Yes, its been tested

[ysbaddaden]

Thank you!