Rename ADDRESS_SANITIZER -> ZSTD_ADDRESS_SANITIZER and same for
MEMORY_SANITIZER. Also set it to 0/1 instead of checking for defined.
This allows the user to override ASAN/MSAN detection for platforms that
don't support it.
Add decompress_sources.h, which includes all the decompression .c files.
This is used for kernel decompression.
Also, add a test which checks that including decompress_sources.h works.