pkg-config errors and workaround

[grantbrown]

Good morning,

I was running into some installation challenges on my university's HPC system, and managed to find a workaround with a few small tweaks to the configure file. Broadly, I think there are two issues:

1. libjpeg should be in the list of things pkg-config should be looking for and providing compiler flags
2. There's some other error getting caught by $? that doesn't actually prevent successful compilation and installation of the package (previously it was getting dumped back out with exit 1 despite finding all the libraries needed).

I'm not 100% sure what is causing that second issue, but perhaps glancing at the workaround can help someone with a deeper knowledge of pkg-config/R package builds.

Hope this is useful to someone.