[libcxxabi] Add back HandleLLVMOptions for out of tree builds

[martell]

Summary

Quick change to review

[EricWF]

Thank you.

[martell]

Just to be clear this causes a bunch of problems for my use case

Run Build Command:"/usr/local/bin/ninja" "cmTC_a0bd6"
[1/2] Building CXX object CMakeFiles/cmTC_a0bd6.dir/CMakeCXXCompilerABI.cpp.obj
[2/2] Linking CXX executable cmTC_a0bd6.exe
FAILED: cmTC_a0bd6.exe 
: && /Users/martell/llvm/usr/bin/x86_64-w64-mingw32-clang++ -v CMakeFiles/cmTC_a0bd6.dir/CMakeCXXCompilerABI.cpp.obj -o cmTC_a0bd6.exe -Wl,--out-implib,libcmTC_a0bd6.dll.a -Wl,--major-image-version,0,--minor-image-version,0   && :
clang version 5.0.0 (trunk 304663) (llvm/trunk 304665)
Target: x86_64--windows-gnu
Thread model: posix
InstalledDir: /Users/martell/llvm/usr/bin
 "/Users/martell/llvm/usr/bin/lld" -flavor gnu -m i386pep -Bdynamic -o cmTC_a0bd6.exe /Users/martell/llvm/usr/x86_64-w64-mingw32/lib/crt2.o /Users/martell/llvm/usr/x86_64-w64-mingw32/lib/crtbegin.o -L/Users/martell/llvm/usr/x86_64-w64-mingw32/lib -L/Users/martell/llvm/usr/lib -L/Users/martell/llvm/usr/x86_64-w64-mingw32/sys-root/mingw/lib CMakeFiles/cmTC_a0bd6.dir/CMakeCXXCompilerABI.cpp.obj --out-implib libcmTC_a0bd6.dll.a --major-image-version 0 --minor-image-version 0 -lc++ -lmingw32 /Users/martell/llvm/usr/lib/clang/5.0.0/lib/windows/libclang_rt.builtins-x86_64.a -lmoldname -lmingwex -lmsvcrt -ladvapi32 -lshell32 -luser32 -lkernel32 /Users/martell/llvm/usr/x86_64-w64-mingw32/lib/crtend.o
error: Unable to find library -lc++

I need to specifically define to even get this far.

-DLLVM_NO_OLD_LIBSTDCXX=TRUE
-DCXX_SUPPORTS_CXX11=TRUE

Not something I think I should have to do to bootstrap a cross compiler.
Can you tell me everything you specifically need from HandleLLVMOptions so I can extract that into libcxxabi's cmake modules in a followup commit.

[EricWF]

Your use case isn't the only use case that exists, far from it.

I don't want to be duplicating LLVM modules we should just be using directly

[martell]

In D33753#772520, @EricWF wrote:

Your use case isn't the only use case that exists, far from it.

I don't want to be duplicating LLVM modules we should just be using directly

I think bootstrapping a cross compiler by cross building libc++abi and libc++ is a pretty generic use case.
Pulling in all of LLVM's cmake modules depends on top of libc++abi hinders cmake detection when cross building libc++abi standalone.

You said before that we needed this for the sanitizer.
Do you know why libc++ doesn't need to import this?

[EricWF]

In D33753#772543, @martell wrote:

In D33753#772520, @EricWF wrote:

Your use case isn't the only use case that exists, far from it.

I don't want to be duplicating LLVM modules we should just be using directly

I think bootstrapping a cross compiler by cross building libc++abi and libc++ is a pretty generic use case.
Pulling in all of LLVM's cmake modules depends on top of libc++abi hinders cmake detection when cross building libc++abi standalone.

Then fix LLVM. The in-tree build should act the same as the out-of-tree build.

[sbc100]

Sorry to revive a very old issue, but this change also breaks my WebAssembly build. libcxx doesn't include this and therefor works fine, its only libcxxabi that breaks.. and if I remove this line it works.

What options does this file add? And does libcxxabi really need them? If so, presumbly we should add this line in libcxx too?

[sbc100]

My problem is that HandleLLVMOptions seems to add a lot of compiler and system check.... seemingly more than are required to build libcxxabi. It seems like by including this line we are maybe needlessly restricting the set of compilers/environments on which it can be built.

[martell]

In D33753#975343, @sbc100 wrote:

My problem is that HandleLLVMOptions seems to add a lot of compiler and system check.... seemingly more than are required to build libcxxabi. It seems like by including this line we are maybe needlessly restricting the set of compilers/environments on which it can be built.

Hey Sam, this was my issue also, In rL304374 I did a refactor on the cmake usage in libcxxabi.
I removed include(HandleLLVMOptions OPTIONAL) which made the change a FC rather then a NFC so I re added this line.
Eric said that this is still needed for out of tree builds, beyond that I don't know any more details as I have never used llvm in this way.

[martell]

Err, I mean Sam, Sorry.

[sbc100]

Looks like this was recently fixed by @phosek in rL354284

libcxxabi/trunk/cmake/Modules/HandleOutOfTreeLLVM.cmake

if (WIN32)
       set(LLVM_ON_WIN32 1)
     else()
       set(LLVM_ON_UNIX 1)
       set(LLVM_ON_WIN32 0)
     endif()
   endif()
   if (LLVM_FOUND)
     include(AddLLVM OPTIONAL)
+    include(HandleLLVMOptions OPTIONAL)
   endif()
 
   # LLVM Options --------------------------------------------------------------
   if (NOT DEFINED LLVM_INCLUDE_TESTS)
     set(LLVM_INCLUDE_TESTS ${LLVM_FOUND})
   endif()
   if (NOT DEFINED LLVM_INCLUDE_DOCS)
     set(LLVM_INCLUDE_DOCS ${LLVM_FOUND})