The static global variables can be disabled if encoders and decoders
are not built. If they are not disabled and -Werror is used, it will
cause an usused warning as an error.
test_bcj_exact_size, test_check, test_hardware, and test_index will
all now compile and skip properly if encoders or decoders are disabled.
Also fixed a small typo (disabed -> disabled).
Thanks to Sebastian Andrzej Siewior.
lzma_vli is unsigned so trying a signed value results in
a compiler warning from -Wsign-conversion. (lzma_vli)-1
equals to LZMA_VLI_UNKNOWN anyway which is the next assertion.
