arch/x86-64: fix cmake compile error

-- Configuring done
CMake Error at cmake/nuttx_add_library.cmake:142 (add_library):
  Cannot find source file:

    /vela/nuttx/libs/libc/machine/x86_64/arch_elf.c
Call Stack (most recent call first):
  libs/libc/CMakeLists.txt:22 (nuttx_add_kernel_library)

Signed-off-by: Neo Xu <[email protected]>

libs/libc/machine/x86_64/CMakeLists.txt

@@ -25,7 +25,7 @@ add_subdirectory(gnu)
 set(SRCS)
 
 if(CONFIG_LIBC_ARCH_ELF)
-  list(APPEND SRCS arch_elf.c)
+  list(APPEND SRCS arch_elf64.c)
 endif()
 
 if(CONFIG_ARCH_SETJMP_H)