build: include internal headers in source list
build: include internal headers in source list

Allows 'make dist-*' targets to generate working tarballs.

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso