Can't build after opencv upgrade

OS X / 10.14.2

```
$ make
g++ -std=c++11 -O2 -fstrict-aliasing -ffast-math `pkg-config --cflags opencv` ssimulacra.cpp `pkg-config --libs-only-L opencv` -lopencv_core -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -o ssimulacra
Package opencv was not found in the pkg-config search path.
Perhaps you should add the directory containing `opencv.pc'
to the PKG_CONFIG_PATH environment variable
No package 'opencv' found
Package opencv was not found in the pkg-config search path.
Perhaps you should add the directory containing `opencv.pc'
to the PKG_CONFIG_PATH environment variable
No package 'opencv' found
ssimulacra.cpp:81:10: fatal error: 'cv.hpp' file not found
#include
^~~~~~~~
1 error generated.
make: *** [ssimulacra] Error 1
```

I’m guessing this is related to the fact that Homebrew recently upgraded my OpenCV to version 4.0.1. I took a stab at fixing it by finding something that looked like `opencv.pc` and symlinking it to that path:

```
$ ln -s /usr/local/Cellar/opencv/4.0.1/lib/pkgconfig/opencv4.pc /usr/local/lib/pkgconfig/opencv.pc
```

That got rid of the first error, but did not fix the second (`fatal error: 'cv.hpp' file not found`).

Any advice? Should I try to install an earlier version of OpenCV?