devel/nspr: update to 4.19 (nop)

From upstream ChangeLog:

• Update NSPR to build with Android NDK r16
• Add missing include for SIZE_MAX
• Use atexit() to register _PR_Fini on OSX

Changes: https://hg.mozilla.org/projects/nspr/shortlog/NSPR_4_19_RTM
ABI: https://abi-laboratory.pro/tracker/timeline/nspr/
MFH: 2018Q1 (required by Firefox 60)