[AArch64] Simplify getcontext pstate initialization.
[AArch64] Adjust elf_machine_dynamic to find _DYNAMIC via _GLOBAL_OFFSET_TABLE_
[BZ #15022] Correct global-scope dlopen issues in static executables.

This change creates a link map in static executables to serve as the
global search list for dlopen.  It fixes a problem with the inability
to access the global symbol object and a crash on an attempt to map a
DSO into the global scope.  Some code that has become dead after the
addition of this link map is removed too and test cases are provided.
Add a dlopen/getpagesize static executable test.