config.h should never be installed; it is bound to cause issues with various other autoconf based packages. The rest of the headers should probably be moved to a namespaced directory under /usr/include.
It looks like this first started happening with ragel-7.x; previous versions did not install any headers.
I think this has been resolved upstream. commit 927f380272442ae803fdccfc001b55877f25e7dc Author: Adrian Thurston <thurston@colm.net> Date: Sat Dec 10 15:41:30 2016 -0500 use pkginclude for the headers aapl/Makefile.am | 2 +- src/Makefile.am | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)
(In reply to Mike Gilbert from comment #2) > I think this has been resolved upstream. Applying that patch by hand in src_prepare does move the installed header files under /usr/include/ragel/ as hoped for.
*** Bug 626156 has been marked as a duplicate of this bug. ***
commit 3da0e31d7df42c829b18f46d9a073de8a1188d9b Author: Luca Barbato <lu_zero@gentoo.org> Date: Sat Dec 23 02:40:24 2017 +0000 dev-util/ragel: Fix the include path Address bug #642016. Package-Manager: Portage-2.3.19, Repoman-2.3.6