Link LLVM dynamically on Windows, deploy Universal CRT dlls.

[vadimcn]

Summary

This addresses LLDB bug 31699, which was caused by LLVM using static linking on Windows.

In order to make sure that LLVM continues to work on machines that do not have the Universal CRT yet, we'll need to ship a copy of UCRT in the Windows installation package. Fortunately, CMake 3.6+ already supports app-local deployment of UCRT dlls, we just need to turn this on.

[rnk]

lgtm

[hans]

Thanks! This sounds good.

Could we make CMAKE_INSTALL_UCRT_LIBRARIES the default when building for Windows? Would there be any downside to that?

[vadimcn]

Could we make CMAKE_INSTALL_UCRT_LIBRARIES the default when building for Windows? Would there be any downside to that?

I don't think it's necessary. People building locally will already UCRT installed since they have MSVC. It's only the "official" builds that might get installed on a bare machine that might need those dlls.
Besides, CMake will mark WINDOWS_KITS_REDIST_DIR path with an error if builder's machine doesn't have a recent version of Windows 10 SDK installed (UCRT was not redistributable until late 2015). This might be confusing.

[hans]

lgtm

llvm/trunk/CMakeLists.txt

foreach(target ${LLVM_DISTRIBUTION_COMPONENTS})
 
     if(TARGET install-${target})
       add_dependencies(install-distribution install-${target})
     else()
       message(FATAL_ERROR "Specified distribution component '${target}' doesn't have an install target")
     endif()
   endforeach()
 endif()
+
+# This allows us to deploy the Universal CRT DLLs by passing -DCMAKE_INSTALL_UCRT_LIBRARIES=ON to CMake
+if (MSVC)
+  include(InstallRequiredSystemLibraries)
+endif()

llvm/trunk/utils/release/build_llvm_package.bat

 svn.exe export -r %revision% http://llvm.org/svn/llvm-project/clang-tools-extra/%branch% llvm/tools/clang/tools/extra || exit /b
 svn.exe export -r %revision% http://llvm.org/svn/llvm-project/lld/%branch% llvm/tools/lld || exit /b
 svn.exe export -r %revision% http://llvm.org/svn/llvm-project/compiler-rt/%branch% llvm/projects/compiler-rt || exit /b
 svn.exe export -r %revision% http://llvm.org/svn/llvm-project/openmp/%branch% llvm/projects/openmp || exit /b
 svn.exe export -r %revision% http://llvm.org/svn/llvm-project/lldb/%branch% llvm/tools/lldb || exit /b
 
 
 REM Setting CMAKE_CL_SHOWINCLUDES_PREFIX to work around PR27226.
-set cmake_flags=-DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_INSTALL_TOOLCHAIN_ONLY=ON -DLLVM_USE_CRT_RELEASE=MT -DCLANG_FORMAT_VS_VERSION=%clang_format_vs_version% -DPACKAGE_VERSION=%package_version% -DLLDB_RELOCATABLE_PYTHON=1 -DLLDB_TEST_COMPILER=%cd%\build32_stage0\bin\clang.exe -DCMAKE_CL_SHOWINCLUDES_PREFIX="Note: including file: "
+set cmake_flags=-DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_INSTALL_TOOLCHAIN_ONLY=ON -DCMAKE_INSTALL_UCRT_LIBRARIES=ON -DCLANG_FORMAT_VS_VERSION=%clang_format_vs_version% -DPACKAGE_VERSION=%package_version% -DLLDB_RELOCATABLE_PYTHON=1 -DLLDB_TEST_COMPILER=%cd%\build32_stage0\bin\clang.exe -DCMAKE_CL_SHOWINCLUDES_PREFIX="Note: including file: "
 
 REM TODO: Run all tests, including lld and compiler-rt.
 
 call "%vcdir%/vcvarsall.bat" x86
 set CC=
 set CXX=
 mkdir build32_stage0
 cd build32_stage0