libc: centralize makecontext symbols

[brooks]

Summary

Declare makecontext() and __makecontext() symbols centrally as they are
always implemented.

lib/libc/aarch64/Symbol.map

 /*
  * This only needs to contain symbols that are not listed in
  * symbol maps from other parts of libc (i.e., not found in
  * stdlib/Symbol.map, string/Symbol.map, sys/Symbol.map, ...).
  */
 FBSD_1.0 {
         .mcount;
         fabs;
         __flt_rounds;
         fpgetmask;
         fpsetmask;
         __infinity;
         __nan;
-        makecontext;
-};
-
-FBSDprivate_1.0 {
-        __makecontext;
 };

lib/libc/amd64/Symbol.map

FBSD_1.0 {
         fpgetprec;
         fpgetround;
         fpgetsticky;
         fpsetmask;
         fpsetprec;
         fpsetround;
         __infinity;
         __nan;
-        makecontext;
         rfork_thread;
         amd64_get_fsbase;
         amd64_get_gsbase;
         amd64_set_fsbase;
         amd64_set_gsbase;
         brk;
         sbrk;
 };

  * FreeBSD private ABI
  *
  */
 FBSDprivate_1.0 {
         /* PSEUDO syscalls */
         _getlogin;
 
         ___longjmp;
-        __makecontext;
         __longjmp;
         __signalcontext;
         signalcontext;
         __siglongjmp;
         _brk;
         _vfork;
 };

lib/libc/arm/Symbol.map

 /*
  * This only needs to contain symbols that are not listed in
  * symbol maps from other parts of libc (i.e., not found in
  * stdlib/Symbol.map, string/Symbol.map, sys/Symbol.map, ...).
  */
 FBSD_1.0 {
         __mcount;
         alloca;
         fabs;
         __infinity;
         __nan;
-        makecontext;
         brk;
         sbrk;
 };
 
 FBSD_1.3 {
         __flt_rounds;
 };
 
 FBSD_1.4 {
         __gnu_Unwind_Find_exidx;
         dl_unwind_find_exidx;
 };
 
 FBSD_1.6 {
         arm_drain_writebuf;
         arm_sync_icache;
 };
 
 FBSDprivate_1.0 {
         /* PSEUDO syscalls */
         _getlogin;
 
         __aeabi_read_tp;
         ___longjmp;
-        __makecontext;
         __longjmp;
         signalcontext;
         _signalcontext;
         __siglongjmp;
         _vfork;
         _brk;
         _sbrk;
 
         _libc_arm_fpu_present;
 };

lib/libc/gen/Symbol.map

FBSD_1.0 {
         __isinfl;
         isatty;
         initgroups;
         jrand48;
         lcong48;
         ldexp;
         lockf;
         lrand48;
+        makecontext;
         modf;
         mrand48;
         nice;
         nlist;
         nrand48;
         opendir;
         pause;
         posix_madvise;
#endif
         __libc_tcdrain;
 
         __elf_aux_vector;
         __pthread_distribute_static_tls;
         __pthread_map_stacks_exec;
         __fillcontextx;
         __fillcontextx2;
         __getcontextx_size;
+        __makecontext;
 };