dave@akai ~ % pkg-config --exists --print-errors libmozjs                                                                                                                                                      
Package libmozjs was not found in the pkg-config search path.
Perhaps you should add the directory containing `libmozjs.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libmozjs' found
dave@akai ~ % echo $PKG_CONFIG_PATH                                                                                                                                                                            

dave@akai ~ % export PKG_CONFIG_PATH=/usr/lib/pkgconfig                                                                                                                                                        
dave@akai ~ % echo $PKG_CONFIG_PATH                                                                                                                                                                            
/usr/lib/pkgconfig

dave@akai ~ % pkg-config --exists --cflags --libs --print-errors mozjs185                                                                                                                                      
Package nspr was not found in the pkg-config search path.
Perhaps you should add the directory containing `nspr.pc'
to the PKG_CONFIG_PATH environment variable
Package 'nspr', required by 'SpiderMonkey 1.8.5', not found
dave@akai ~ % locate nspr | grep pc                                                                                                                                                                            
/usr/local/Cellar/nspr/4.8.8/include/nspr/pripcsem.h

dave@akai ~ % /usr/local/Cellar/nspr/4.8.8/bin/nspr-config --libs --cflags                                                                                                                                     
-I/usr/local/Cellar/nspr/4.8.8/include/nspr
-L/usr/local/Cellar/nspr/4.8.8/lib -lplds4 -lplc4 -lnspr4
dave@akai ~ % brew versions nspr                                                                                                                                                                               
4.8.8    git checkout d3f3554 /usr/local/Library/Formula/nspr.rb
4.8.6    git checkout b782d9d /usr/local/Library/Formula/nspr.rb
4.8.4    git checkout bdb9280 /usr/local/Library/Formula/nspr.rb
4.7.6    git checkout 135972d /usr/local/Library/Formula/nspr.rb
4.7.5    git checkout a82e823 /usr/local/Library/Formula/nspr.rb

dave@akai ~ % brew uninstall nspr                                                                                                                                                                              
Uninstalling /usr/local/Cellar/nspr/4.8.8...
dave@akai ~ % brew install nspr                                                                                                                                                                                
==> Downloading http://ftp.mozilla.org/pub/mozilla.org/nspr/releases/v4.8.8/src/nspr-4.8.8.tar.gz
######################################################################## 100.0%
==> ./configure --prefix=/usr/local/Cellar/nspr/4.8.8 --disable-debug --enable-strip --enable-optimize --enable-64bit
==> make
==> make install
Warning: Non-executables were installed to "bin".
Installing non-executables to "bin" is bad practice.
The offending files are:
/usr/local/Cellar/nspr/4.8.8/bin/prerr.properties
Warning: m4 macros were installed to "share/aclocal".
Homebrew does not append "/usr/local/share/aclocal"
to "/usr/share/aclocal/dirlist". If an autoconf script you use
requires these m4 macros, you'll need to add this path manually.
==> Summary
/usr/local/Cellar/nspr/4.8.8: 99 files, 1.6M, built in 14 seconds
dave@akai ~ % mdf nspr | grep pc                                                                                                                                                                               
/usr/local/Cellar/nspr/4.8.8/lib/pkgconfig/nspr.pc
dave@akai ~ % pkg-config --exists --cflags --libs --print-errors mozjs185                                                                                                                                      
dave@akai ~ % pkg-config --cflags --libs --print-errors mozjs185                                                                                                                                               
-I/usr/local/Cellar/spidermonkey/1.8.5/include/js -I/usr/local/include/nspr  -L/usr/local/Cellar/spidermonkey/1.8.5/lib -L/usr/local/lib -lmozjs185 -lplds4 -lplc4 -lnspr4  
dave@akai ~ % pkg-config --libs --print-errors mozjs185                                                                                                                                                        
-L/usr/local/Cellar/spidermonkey/1.8.5/lib -L/usr/local/lib -lmozjs185 -lplds4 -lplc4 -lnspr4  
dave@akai ~ %