Switching back to pure C language implementation

Fixes #2. Conformance test report:

 - Pass hello world test for both dynamically and statically linked exec

 - Pass bionic-unit-tests-static/bionic-unit-tests test.
   NOTE:
   + The pthread.pthread_setname_np__no_such_thread may fail because of
     timing issue.
     The original bionic has same issue, too.
   + In ARM/Linux environment, the following items would fail as same as
     original bionic on ARM/Linux.
     * netdb.getaddrinfo_NULL_hints
     * pthread.pthread_key_create_lots
     * getpwnam.system_id_root
     * getpwnam.system_id_system
     * getpwnam.app_id_radio
     * getpwnam.app_id_nobody
     * getpwnam.app_id_all_a0
     * getpwnam.app_id_u1_a40000
     * getpwnam.app_id_u0_a0
     * getpwnam.app_id_u0_a1234
     * getpwnam.app_id_u0_a9999
     * getpwnam.app_id_u1_root
     * getpwnam.app_id_u1_radio
     * getpwnam.app_id_u1_a0
     * getpwnam.app_id_u1_i0

Signed-off-by: Jim Huang <jserv@0xlab.org>