r600g/sb: get rid of standard c++ streams

Static initialization of internal libstdc++ data related to iostream
causes segfaults with some apps.

This patch replaces all uses of std::ostream and std::ostringstream in sb
with custom lightweight classes.

Prevents segfaults with ut2004demo and probably some other old apps.

Signed-off-by: Vadim Girlin <vadimgirlin@gmail.com>

src/gallium/drivers/r600/sb/sb_context.cpp

@@ -28,6 +28,8 @@
 
 namespace r600_sb {
 
+sb_log sblog;
+
 unsigned sb_context::dump_pass = 0;
 unsigned sb_context::dump_stat = 0;
 unsigned sb_context::dry_run = 0;