[Fuchsia][CMake] Set output name for libc++ shared library (#111791)

This is a dependency of #80007.

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -345,6 +345,7 @@ foreach(target armv6m-none-eabi;armv7m-none-eabi;armv8m.main-none-eabi)
   set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_SHARED_OUTPUT_NAME "c++-shared" CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_LIBC "llvm-libc" CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")
@@ -396,6 +397,7 @@ foreach(target riscv32-unknown-elf)
   set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
+  set(RUNTIMES_${target}_LIBCXX_SHARED_OUTPUT_NAME "c++-shared" CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_LIBC "llvm-libc" CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_FILESYSTEM OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_RANDOM_DEVICE OFF CACHE BOOL "")