update newlib glue for use with vfscore

Consists of multiple fixes:
  - remove stubs of the functions provided by vfscore
  - import mount.h, statfs.h, uio.h from nolibc (minimal changes)
  - add stub for sigfillset

Signed-off-by: Yuri Volchkov <yuri.volchkov@neclab.eu>
Reviewed-by: Florian Schmidt <florian.schmidt@neclab.eu>

Add missing include to time.c

time.c uses errno, but doesn't include the correct header.

Signed-off-by: Florian Schmidt <florian.schmidt@neclab.eu>
Reviewed-by: Felipe Huici <felipe.huici@neclab.eu>

Fix remaining time in nanosleep

Add the fix of commit 96f68ab in unikraft to newlib:
Calculate the remaining time to sleep and update
the rem parameter if it is given.
If the remaining time is larger than 0, it means that
the thread was waken up explicitly and nanosleep returns -1
to indicate that. Otherwise nanosleep returns 0.

Signed-off-by: Dafna Hirschfeld <dafna3@gmail.com>
Reviewed-by: Florian Schmidt <florian.schmidt@neclab.eu>

reimplement nanosleep for new api

Signed-off-by: Yuri Volchkov <yuri.volchkov@neclab.eu>
Signed-off-by: Simon Kuenzer <simon.kuenzer@neclab.eu>
Reviewed-by: Simon Kuenzer <simon.kuenzer@neclab.eu>

remove functions provided by libvfscore

Which are: close, read and write

Signed-off-by: Yuri Volchkov <yuri.volchkov@neclab.eu>
Reviewed-by: Simon Kuenzer <simon.kuenzer@neclab.eu>

patch: set default _READ_WRITE_RETURN_TYPE to _ssize_t

The vfscore provides the same definitions of functions read/write as
in 'man 2 write'. Newlib used int as a return type of these functions,
which is wrong.

Signed-off-by: Yuri Volchkov <yuri.volchkov@neclab.eu>
Reviewed-by: Simon Kuenzer <simon.kuenzer@neclab.eu>

build: add CONFIG_ prefix to all kconfig symbols

This is needed to support similar modifications in Unikraft main repo

Signed-off-by: Yuri Volchkov <yuri.volchkov@neclab.eu>
Reviewed-by: Simon Kuenzer <simon.kuenzer@neclab.eu>

Initial public release: documentation

This contains the initial documentation for newlib for Unikraft.

Signed-off-by: Florian Schmidt <florian.schmidt@neclab.eu>

Initial public release: configuration and build files

This contains the configuration and make files required to build
libnewlib for Unikraft.

Signed-off-by: Simon Kuenzer <simon.kuenzer@neclab.eu>

Initial public release: glue code

This contains the glue/wrapper code required to build libnewlib for
Unikraft.

Signed-off-by: Felipe Huici <felipe.huici@neclab.eu>
Signed-off-by: Florian Schmidt <florian.schmidt@neclab.eu>

initial commit (empty)

Signed-off-by: Florian Schmidt <florian.schmidt@neclab.eu>