ASSERT "instr_encode error: no encoding found" on syscalls_win test on win8

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on June 20, 2014 12:16:58_

http://build.chromium.org/p/client.drmemory/builders/win-8_x64-drm/builds/1009/steps/Dr.%20Memory%20ctest/logs/stdio 59: STDERR:
59:
59:
59: ~~Dr.M~~ Dr. Memory version 1.6.1955
59: ~~Dr.M~~ Running "./syscalls_win.exe"
59:
59:
59:
59: ~~Dr.M~~ WARNING: application exited with abnormal code 0xffffffff
59:
59:
59: CMake Error at runtest.cmake:312 (message):
59: *_*
59: .././bin/drmemory.exe;-debug;-dr_debug;-dr;E:/b/build/slave/win-8_x64-drm/build/build_drmemory-dbg-32/dynamorio;-batch;-dr_ops;-dumpcore_mask
59: 0x87fd -stderr_mask 15 -msgbox_mask
59: 0;-callstack_style;0x27;-no_results_to_stderr;--;./syscalls_win.exe failed
59: (-1): Test sysarg size in field: done
59:
59: Test NtUser[Set/Get]KeyboardState: done
59:
59: Test NtCreatePrivateNamespaces: done
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59:
59:
59:
59:
59:
59:
59: ~~Dr.M~~ Dr. Memory version 1.6.1955
59:
59: ~~Dr.M~~ Running "./syscalls_win.exe"
59:
59:
59:
59:
59:
59:
59:
59:
59: ~~Dr.M~~ WARNING: application exited with abnormal code 0xffffffff
59:
59: *_*
59:
59:
59:
71/85 Test `#59`: syscalls_win .....................***Failed 5.91 sec

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1570_