Fix compiling warnings.
Fix one reg collision in BC_TSETS.
Fix BC_TGETV/TSETV bug.

We could pass bootstrap stage 1, luajit could execute Dynasm module
in simple way, for example, parse arguments and show help, like the
following:

[jiwang@bjgwc-5 luajit-2.0]$ ./src/luajit dynasm/dynasm.lua
DynASM -- A dynamic assembler for code generation engines.
DynASM 1.3.0 2011-05-05  http://luajit.org/dynasm.html

  Usage: dynasm [OPTION]... INFILE.dasc|-

    -h, --help           Display this help text.
    -V, --version        Display version and copyright information.

    -o, --outfile FILE   Output file name (default is stdout).
    -I, --include DIR    Add directory to the include search path.

To fully bootstrap, we need to implement another bunch of runtime
helper assembly templates, i.e. lj_ffNNNN, which has not been triggered
previously.