nspr: Update to 4.27

Changelog:
NSPR 4.27 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.
- An include statement for a Windows system library header
  was added

(ryoon)