[libcxxabi] Always link against libzircon for Fuchsia targets (#115910)

When using LTO, the deplibs mechanism is insufficient to ensure that
libzircon is always brought into the link prior to LTO code generation.
The general problem is discussed in depth in
#56070

To work around this, we can just provide libzircon as a link input.

Author: ilovepi

libcxxabi/src/CMakeLists.txt

@@ -75,6 +75,12 @@ if (NOT APPLE) # On Apple platforms, we always use -nostdlib++ so we don't need
   add_library_flags_if(LIBCXXABI_HAS_C_LIB c)
 endif()
 
+if (FUCHSIA)
+    # TODO: Use CMAKE_LINK_LIBRARY_USING_FEATURE once our minimum CMake is at least 3.24
+    # https://cmake.org/cmake/help/latest/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.html 
+    add_link_flags("-Wl,--push-state,--as-needed,-lzircon,--pop-state")
+endif()
+
 if (NOT LIBCXXABI_USE_COMPILER_RT)
   add_library_flags_if(LIBCXXABI_HAS_GCC_LIB gcc)
 endif()