runtime: Link libatomic on 64-bit RISC-V and LoongArch (#4864)

Fixes #4847.

Author: kinke

runtime/CMakeLists.txt

@@ -141,6 +141,10 @@ if("${C_SYSTEM_LIBS}" STREQUAL "AUTO")
         else()
             set(C_SYSTEM_LIBS m pthread)
         endif()
+        # some archs need libatomic for 128-bit CAS druntime unittests
+        if(CMAKE_SYSTEM_PROCESSOR MATCHES "riscv64|loongarch64")
+            set(C_SYSTEM_LIBS atomic ${C_SYSTEM_LIBS})
+        endif()
         set(C_SYSTEM_LIBS_SHARED ${C_SYSTEM_LIBS})
     endif()
 else()