3ds: Various fixes, optimizations.

This commit does the following changes:

- Fix mkdir implementation not reporting EEXIST error.
- Fix database build feature.
- Small speed-up when parsing directories and files.
- Fix buffering thread hogging cpu and preventing other threads to run.
- Fix sdl plugins not compiling by re-adding ctru specific cflags in sdl.make.

Change-Id: I507c0dcc85cdbcc607ab9c9c6d0b42e6a80caa5a

apps/plugins/sdl/sdl.make

@@ -39,6 +39,12 @@ SDLFLAGS = -I$(SDL_SRCDIR)/include $(filter-out -O%,$(PLUGINFLAGS))		\
 #-ffast-math -funroll-loops -fomit-frame-pointer -fexpensive-optimizations	\
 #-D_GNU_SOURCE=1 -D_REENTRANT -DSDL -DELF
 
+# CTRU does need these to avoid compiler errors
+ifeq ($(APP_TYPE),ctru-app)
+SDLFLAGS += -Wno-int-conversion -Wno-incompatible-pointer-types        \
+-Wno-implicit-function-declaration -Wno-implicit-int
+endif
+
 ifndef APP_TYPE
     ### no target has a big enough plugin buffer
     ROCKS += $(SDL_OBJDIR)/duke3d.ovl