[runtime][CMake] use static_library try compile

[jsji]

Summary

We were using static library trycompile in compiler-rt, eg:

compiler-rt/lib/builtins/CMakeLists.txt:
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
compiler-rt/cmake/Modules/AddCompilerRT.cmake:
-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY

We should also use it in runtime build.
Or else CMake may not be able to detect ABI and others correctly when
configuring compiler-rt.

eg: On AIX, we can't build compiler-rt without this fix in runtime build,
linking CMakeCCompilerABI.c will fail hence failing to detect ABI.

[phosek]

See this thread https://groups.google.com/g/llvm-dev/c/KWy1-Dw_9Rk, as I mentioned there I don't think we can set CMAKE_TRY_COMPILE_TARGET_TYPE unconditionally to STATIC_LIBRARY because doing so is going to disable some checks which may cause issues for some targets.

You should be able to bypass the failing ABI detection by setting CMAKE_{C,CXX,ASM}_COMPILER_WORKS to ON.

[jsji]

In D98894#2635838, @phosek wrote:

See this thread https://groups.google.com/g/llvm-dev/c/KWy1-Dw_9Rk, as I mentioned there I don't think we can set CMAKE_TRY_COMPILE_TARGET_TYPE unconditionally to STATIC_LIBRARY because doing so is going to disable some checks which may cause issues for some targets.

You should be able to bypass the failing ABI detection by setting CMAKE_{C,CXX,ASM}_COMPILER_WORKS to ON.

Thanks for the info. I will do some more experiments then.

[jsji]

This only *workaround* the failure in AIX runtime build, which we should fix in AIX runtime, so this is not required. Thanks Petr.

runtimes/CMakeLists.txt

 # This file handles building LLVM runtime sub-projects.
 cmake_minimum_required(VERSION 3.13.4)
+set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
 project(Runtimes C CXX ASM)
 
 set(LLVM_ALL_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind;openmp")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )
   set(LLVM_ENABLE_RUNTIMES ${LLVM_ALL_RUNTIMES})
 endif()