Only enable shared libc++ for ASan, MSan, TSan and UBSan-vptr builds.

Re-land of https://codereview.chromium.org/2978723002 with a fix
for UBSan.

Bug: 701919
Change-Id: I75f798dab00c966d8a1ecdebc519a0251f914700
Reviewed-on: https://chromium-review.googlesource.com/572186Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486931}

build/config/c++/c++.gni

@@ -11,8 +11,13 @@ declare_args() {
   use_custom_libcxx = (is_linux && !is_chromeos &&
                        (!is_chromecast || is_cast_desktop_build)) || is_msan
 
-  # Sanitizer builds need to override operator new, operator delete, and
-  # some exception handling symbols, so libc++ must be a shared library
-  # to prevent duplicate symbol errors when linking.
-  libcpp_is_static = !is_component_build && !using_sanitizer
+  # ASan, MSan and TSan builds need to override operator new, operator delete,
+  # and some exception handling symbols, so libc++ must be a shared library to
+  # prevent duplicate symbol errors when linking.
+  # Additionally, -fsanitize=vptr requires libc++ to be a shared library
+  # because the ubsan runtime library that implements -fsanitize=vptr calls
+  # dynamic_cast with the ABI type info classes, which won't return the right
+  # answer if each DSO has its own copy of the ABI classes.
+  libcpp_is_static = !is_component_build && !is_asan && !is_msan && !is_tsan &&
+                     !is_ubsan && !is_ubsan_security && !is_ubsan_vptr
 }