Fix Makefile.in

* Remove -Os from the CFLAGS (already handled by Buildroot)
* Use $(CC) instead of $(CPP) to generate .depend file because
  '$(CPP) -M' call does not support multiple input files.
  This avoid the following error:

make[1]: Entering directory `/opt/br/output/build/newt-0.51.0'
/opt/br/output/host/usr/bin/arm-none-linux-gnueabi-cpp -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -M newt.c button.c form.c checkbox.c entry.c label.c listbox.c scrollbar.c textbox.c scale.c grid.c windows.c buttonbar.c checkboxtree.c > .depend
arm-none-linux-gnueabi-cpp: too many input files
make[1]: *** [depend] Error 1
make[1]: Leaving directory 
`/opt/br/output/build/newt-0.51.0'
make: *** 
[/opt/br/output/build/newt-0.51.0/.stamp_built] Error 2


Signed-off-by: Samuel Martin <s.martin49@gmail.com>

---
Index: newt-0.51.0/Makefile.in
===================================================================
--- newt-0.51.0.orig/Makefile.in	2012-10-10 22:43:42.042318041 +0200
+++ newt-0.51.0/Makefile.in	2012-10-11 21:25:44.063873277 +0200
@@ -3,7 +3,7 @@ SHLIBS = -lslang -lm -lc
 
 GPM_SUPPORT=@gpm_support@
 
-CFLAGS = -Wall -Os -D_GNU_SOURCE
+CFLAGS += -D_GNU_SOURCE
 
 VERSION = @VERSION@
 CVSTAG = r$(subst .,-,$(VERSION))
@@ -86,7 +86,7 @@ clean:
 		$(SHAREDOBJS) *.so*
 
 depend:
-	$(CPP) $(CFLAGS) -M $(SOURCES) > .depend
+	$(CC) $(CFLAGS) -M $(SOURCES) > .depend
 
 $(SHAREDDIR):
 	mkdir -p $(SHAREDDIR)