rstan warning messages

Are you trying to build R and components for i686 rather than x86_64?

Never mind. Your logs make it clear that you're building for x86_64.

Can you share the output of:

pkg-config --list-all |grep libcurl
curl-config --libs
rpm -V libcurl-devel libcurl

I'm honestly baffled as to why the configure script is failing to find
libcurl.pc on your system:

  Package libcurl was not found in the pkg-config search path.

  Perhaps you should add the directory containing `libcurl.pc'

  to the PKG_CONFIG_PATH environment variable

  No package 'libcurl' found

Do you have any files installed into /usr/local/ ?

~tom

==
Red Hat