Hello,

I'm on a pretty recent version of Ubuntu (18.04.3 LTS).
I installed clang-9 (which installs llvm-9). The same problem appears
with clang-6.0.

I followed the build process for the devel branch, as described in
https://github.com/bondhugula/pluto
The process blocks while running ./configure (with no arguments). Here are
the last lines it prints:
checking which clang to use... system
checking for llvm-config... yes
checking for main in -lLLVM-9.0.0... yes
checking clang/Basic/SourceLocation.h usability... no
checking clang/Basic/SourceLocation.h presence... no
checking for clang/Basic/SourceLocation.h... no
configure: error: clang header file not found
checking for pet/Makefile... no
configure: error: configure in pet/ failed

To get to this point, I also had to make symbolic links to FileCheck-9 and
llvm-config-9 to get rid of the "-9" (otherwise, the installation build blocks
earlier, as it requires FileCheck and llvm-config without the version number).

Addendum: the stable version compiles with no problems.

Best,
dpotop