reinstate bits/uClibc_arch_features.h in installed headers,

my cross-compile toolchain based on gcc 4.3.1 broke without it.

Makefile.in

@@ -220,7 +220,8 @@ install_headers: headers $(top_builddir)extra/scripts/unifdef
 	$(RM) $(PREFIX)$(DEVEL_PREFIX)include/bits/atomic.h
 	$(RM) $(PREFIX)$(DEVEL_PREFIX)include/bits/sigcontextinfo.h
 	$(RM) $(PREFIX)$(DEVEL_PREFIX)include/bits/stackinfo.h
-	$(RM) $(PREFIX)$(DEVEL_PREFIX)include/bits/uClibc_arch_features.h
+	# gcc 4.3.1 needs it, dont rm:
+	#$(RM) $(PREFIX)$(DEVEL_PREFIX)include/bits/uClibc_arch_features.h
 ifneq ($(UCLIBC_HAS_FLOATS),y)
 	# Remove floating point related headers since float support is disabled.
 	$(RM) $(PREFIX)$(DEVEL_PREFIX)include/complex.h