/usr/lib/x86_64-linux-gnu/pkgconfig/nspr.pc is in libnspr4-dev 2:4.13.1-0ubuntu0.16.04.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | prefix=/usr
exec_prefix=${prefix}
libdir=/usr/lib/x86_64-linux-gnu
includedir=${prefix}/include/nspr
Name: NSPR
Description: The Netscape Portable Runtime
Version: 4.13.1
Libs: -L/usr/lib/x86_64-linux-gnu -lplds4 -lplc4 -lnspr4
Cflags: -I${prefix}/include/nspr
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