[CMake][Fuchsia] Pass -ldl -lpthread LDFLAGS to second stage

We're using static libc++ for the second stage which requires explicitly
linking -ldl and -lpthread.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@353853 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/caches/Fuchsia.cmake

@@ -74,6 +74,12 @@ if(BOOTSTRAP_CMAKE_SYSTEM_NAME)
   endif()
 endif()
 
+if(UNIX)
+  set(BOOTSTRAP_CMAKE_SHARED_LINKER_FLAGS "-ldl -lpthread" CACHE STRING "")
+  set(BOOTSTRAP_CMAKE_MODULE_LINKER_FLAGS "-ldl -lpthread" CACHE STRING "")
+  set(BOOTSTRAP_CMAKE_EXE_LINKER_FLAGS "-ldl -lpthread" CACHE STRING "")
+endif()
+
 set(BOOTSTRAP_LLVM_ENABLE_LTO ON CACHE BOOL "")
 if(NOT APPLE)
   set(BOOTSTRAP_LLVM_ENABLE_LLD ON CACHE BOOL "")