Do not require picins.sty.
https://bugs.gentoo.org/577828#c4

--- gnuplot/docs/Makefile.am
+++ gnuplot/docs/Makefile.am
@@ -143,9 +143,10 @@
 	$(AM_V_at)GNUPLOT_LIB=$(top_srcdir)/demo $(GNUPLOT_EXE) $(srcdir)/plotstyles.gnu
 	rm -f gpinsetfigure.tex
 	printf '%s\n' '\usepackage{graphicx}' \
-		'\usepackage{picins}' \
 		'\newcommand{\gpinsetfigure}[1]{' \
-		'  \parpic[r][rt]{\includegraphics[width=3in,keepaspectratio]{#1}}' \
+		'  \begin{figure}[htb]' \
+		'  \centering\includegraphics[width=3in,keepaspectratio]{#1}' \
+		'  \end{figure}' \
 		'}' > gpinsetfigure.tex
 	$(AM_V_GEN)touch $@
 	$(AM_V_at)touch figurestyle