Installation output for sdl2-ttf [fail]

Installation time: 2s

'/usr/home/chicken/salmonella/build/salmonella-run-publish/chicken/bin/chicken-install' -v 2>&1
checking sdl2-ttf ...
checking platform for `sdl2-ttf'
checking dependencies for `sdl2-ttf'
 missing: sdl2
resolving alias `kitten-technologies' to: http://chicken.kitten-technologies.co.uk/henrietta.cgi
resolving alias `call-cc' to: http://code.call-cc.org/cgi-bin/henrietta.cgi
listing versions for sdl2: http://chicken.kitten-technologies.co.uk/henrietta.cgi
connecting to host "chicken.kitten-technologies.co.uk", port 80 ...
requesting "/henrietta.cgi?name=sdl2&release=5&mode=default&listversions=1" ...
reading response ...
HTTP/1.1 200 OK
Date: Sat, 25 May 2019 23:52:00 GMT
Server: Apache/2.2.31 (Unix) DAV/2 PHP/5.5.36 mod_fastcgi/2.4.6
Connection: close
Transfer-Encoding: chunked
Content-Type: text/plain
reading chunks .
reading response ...
sdl2 located at /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2
checking sdl2 ...
checking platform for `sdl2'
checking dependencies for `sdl2'
install order:
("sdl2" "sdl2-ttf")
building sdl2
running script /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2.build.sh
executing: "sh /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2.build.sh"
   /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/custom-build.sh -host -D compiling-extension -J -s -regenerate-import-libraries -setup-mode -I /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2 -C -I/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2 -O2 -d1 sdl2-features.scm -o /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2-features.so
/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2-features.c:10:10: fatal error: 'SDL.h' file not found
#include "SDL.h"
         ^~~~~~~
1 error generated.

Error: shell command terminated with non-zero exit status 256: 'clang' '/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2-features.c' -o '/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2-features.o' -c  -fno-strict-aliasing -fwrapv -DHAVE_CHICKEN_CONFIG_H -DC_ENABLE_PTABLES -Os -fomit-frame-pointer -fPIC -DPIC -DC_SHARED -I/usr/local/include/db6 -I/usr/local/include -I/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2 -I/usr/home/chicken/salmonella/build/salmonella-run-publish/chicken/include/chicken -I'/usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/include/chicken'

Error: shell command terminated with nonzero exit code
256
"sh /usr/home/chicken/salmonella/build/salmonella-run-publish/salmonella-repo/repo/cache/sdl2/sdl2.build.sh"