config: UCLIBC_HAS_OBSTACK to optionally enable obstack support

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
libc/misc/gnu/obprintf.c: implement obstack_printf and obstack_vprintf

This adds a straight forward implementation for obstack_printf and
obstack_vprintf on uClibc's already existing obstack_grow and
vasprintf.  It does not attempt to port over glibc's implementation
in terms of _IO_* structs and functions.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
libc: hide obstack relocations

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>