[CMake] Disable libc++ and libc++abi new/delete definitions when built with ASan

[phosek]

Summary

ASan provides its own operator new/delete to intercept all allocations
and deallocations. Currently, they rely on overriding weak symbols that
are already provided by libc++abi and libc++, but that solution is
fragile and breaks in certain scenarios, e.g. when libc++abi is
statically linked into a shared libc++.

Rather we should avoid providing new/delete operators when built with
ASan altogether and rely on new/delete operators provided by the
sanitizer runtime.

[mcgrathr]

IMHO the library code should use #if !__has_feature(...) to avoid the definitions entirely when built with a sanitizer whose runtime provides them.
But this is a fine way to achieve that while we wait for those libraries to be fixed for sanitized builds.

[phosek]

In D60235#1454152, @mcgrathr wrote:

IMHO the library code should use #if !__has_feature(...) to avoid the definitions entirely when built with a sanitizer whose runtime provides them.
But this is a fine way to achieve that while we wait for those libraries to be fixed for sanitized builds.

I agree, D60176 implements that but @ldionne thinks that we should go with the CMake option.

[phosek]

No longer needed, this was done as part of D60926.

clang/cmake/caches/Fuchsia-stage2.cmake

foreach(target x86_64;aarch64)
     set(RUNTIMES_${target}-fuchsia_LIBCXXABI_INSTALL_STATIC_LIBRARY OFF CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY OFF CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY OFF CACHE BOOL "")
     set(RUNTIMES_${target}-fuchsia_LIBCXX_ABI_VERSION 2 CACHE STRING "")
 
+    set(RUNTIMES_${target}-fuchsia-asan_LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-fuchsia-asan_LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
+
     # Use .build-id link.
     list(APPEND RUNTIME_BUILD_ID_LINK "${target}-fuchsia")
   endforeach()
 
   set(LLVM_RUNTIME_SANITIZERS "Address" CACHE STRING "")
   set(LLVM_RUNTIME_SANITIZER_Address_TARGETS "x86_64-fuchsia;aarch64-fuchsia" CACHE STRING "")
 endif()