[Sanitizers, CMake] Also use version script for libclang_rt.asan-i386.so

[ro]

Summary

When building LLVM on x86_64-pc-linux-gnu (Fedora 25) with the bundled gcc 6.4.1
which uses gld 2.26.1-1.fc25, the dynamic/Asan-i386-calls-Dynamic-Test and
dynamic/Asan-i386-inline-Dynamic-Test tests failed to link with

/usr/bin/ld: /var/scratch/gcc/llvm/dist/lib/clang/6.0.0/lib/linux/libclang_rt.asan-i386.so: fork: invalid version 21 (max 0)
/var/scratch/gcc/llvm/dist/lib/clang/6.0.0/lib/linux/libclang_rt.asan-i386.so: error adding symbols: Bad value

I tried building with a self-compiled gcc 7.1.0 using gld 2.28, but the error remained.

It seems the error has been hit before (cf. https://reviews.llvm.org/rL314085), but
no real explanation has been found.

However, the problem goes away when linking the i386 libclang_rt.asan with a version
script just like every other variant is. Not using the version script in this single case
dates back to the initial introduction of the version script in r236551, but this change
was just checked in without any explanation AFAICT.

Since I've not found any other workaround and no reason for not always using the
version script, I propose to do so.

Tested on x86_64-pc-linux-gnu.

[eugenis]

Yeah, I've always wondered about the reason for the special case. Lets see what happens. Please be ready to revert if the bots don't like this.

[ro]

Fine, thanks. However, I still need someone to commit (and eventually revert) this for me.

[eugenis]

I can do that.

lib/asan/CMakeLists.txt

add_compiler_rt_runtime(clang_rt.asan-preinit
     STATIC
     ARCHS ${ASAN_SUPPORTED_ARCH}
     OBJECT_LIBS RTAsan_preinit
     CFLAGS ${ASAN_CFLAGS}
     DEFS ${ASAN_COMMON_DEFINITIONS}
     PARENT_TARGET asan)
 
   foreach(arch ${ASAN_SUPPORTED_ARCH})
-    if (UNIX AND NOT ${arch} STREQUAL "i386")
+    if (UNIX)
       add_sanitizer_rt_version_list(clang_rt.asan-dynamic-${arch}
                                     LIBS clang_rt.asan-${arch} clang_rt.asan_cxx-${arch}
                                     EXTRA asan.syms.extra)
       set(VERSION_SCRIPT_FLAG
            -Wl,--version-script,${CMAKE_CURRENT_BINARY_DIR}/clang_rt.asan-dynamic-${arch}.vers)
       set_property(SOURCE
         ${CMAKE_CURRENT_BINARY_DIR}/dummy.cc
         APPEND PROPERTY