Add ENTRY_PRIVATE for x86
Hidden symbol "_exit_with_stack_teardown"

 - _exit_with_stack_teardown only use in pthread_exit
Mark fake_gmtime_r and fake_localtime_r as static function
Hidden symbol " __findenv"
Fix prototype declare in libc_init_common.h

 - `#if defined(__cplusplus)` is unreasonable for olibc since olibc
   is pure C implementation.
Hidden pthread internal functions
Hidden libm internal functions
Hidden stdio internal functions