Add option to generate compressed backtrace info.

Add flag --generate-mini-debug-info which generates
LZMA compressed .symtab and .debug_frame, which are
sufficient to print java backtraces in libunwind.

If enabled, it increases the size of boot.oat by about 3.5%.

Change-Id: Ic3c2ef7704c05fa328720c6781ca2a9b8e3935a3