The fix for gperf in 0ae19f0ced added the generated header to
EXTRA_DIST but that's already added to the distribution because it is
contained in *_SOURCES, what was not added, though, was the .h.in file.
Also fixes the reference to the header file in the .c rule here and for
stroke in out-of-tree builds.
Fixes: 0ae19f0ced ("configure: Fix gperf length parameter determination")