newlib-4.0.0 snapshot created

I have bumped up the newlib release to 4.0.0.  The major release bump was
due to a change to the time.h header file which moved the __tzrule_struct
to a separate header.  A snapshot has been added to the regular newlib
download location.

Special thanks to Corinna for reviewing all the changes and to all who
contributed.

From the NEWS file:

*** Major changes in newlib version 4.0.0:

- additional out-of-bounds checking for malloc/nano-malloc family
- various fixes to makedocbook for python 3.8
- multiple standard/accuracy fixes to libm math routines
- C-SKY port
- support for Armv8-R aarch64 added
- move of __tzrules_struct from time.h to internal header
- math additions/improvements for RISC-V and arm
- all arm code converted to use unified syntax for Thumb1
- fenv support added for multiple platforms
- hard float support for PowerPC taken from FreeBSD
- advertising clause removed from BSD licenses
- various other fixes

-- Jeff J.