[ANNOUNCE] NSPR 4.21.1 Release

[Kai Engert]

The NSPR 4.21.1 release is now available. The hg tag is
NSPR_4_21_1_RTM. The source tar file can be downloaded from
https://ftp.mozilla.org/pub/mozilla.org/nspr/releases/v4.21.1/src/

NSPR 4.21.1 is a patch release for NSPR 4.21, to support
Firefox ESR 68.x and Thunderbird 68.x

NSPR 4.21.1 contains the following changes:
- The macOS platform code for shared library loading was
changed to support macOS 11.
If the absolute path parameter given to PR_LoadLibrary
begins with either /System/ or /usr/lib/ then no test is
performed if the library exists at a file.

For details, please refer to
https://bugzilla.mozilla.org/show_bug.cgi?id=1652956

Thanks to all contributors to this release.
Kai