Rename struct lzma_stream to avoid clash with system header

Rename struct lzma_stream to avoid clash with system header

/home/pedro/gdb/mygit/src/gdb/minidebug.c: At global scope:
/home/pedro/gdb/mygit/src/gdb/minidebug.c:55:8: error: using typedef-name ‘lzma_stream’ after ‘struct’
 struct lzma_stream
        ^
In file included from /usr/include/lzma.h:281:0,
                 from /home/pedro/gdb/mygit/src/gdb/minidebug.c:28:
/usr/include/lzma/base.h:498:3: note: ‘lzma_stream’ has a previous declaration here
 } lzma_stream;
   ^

gdb/ChangeLog:
2015-02-27  Tom Tromey  <tromey@redhat.com>

	* minidebug.c (struct lzma_stream): Rename to ...
	(struct gdb_lzma_stream): ... this.
	(lzma_open, lzma_pread, lzma_close, lzma_stat): Adjust.