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

--- gnuplot-5.0.6-orig/docs/Makefile.am
+++ gnuplot-5.0.6/docs/Makefile.am
@@ -189,7 +189,6 @@
 	  touch figures.idx ; \
 	  rm -f pdffigures.tex ; \
 	  ( echo "\usepackage{graphicx}" > pdffigures.tex ; \
-	    echo "\usepackage{picins}" >> pdffigures.tex ; \
 	  ) ; \
 	  TEXINPUTS=.:$(srcdir):$(top_srcdir):${TEXINPUTS}: $(PDFLATEX) $< ; \
 	  TEXINPUTS=.:$(srcdir):$(top_srcdir):${TEXINPUTS}: $(PDFLATEX) $< ; \
--- gnuplot-5.0.6-orig/docs/doc2tex.c
+++ gnuplot-5.0.6/docs/doc2tex.c
@@ -170,9 +170,9 @@
     case 'F':			/* embedded figure */
 	    if (figures) {
 		line[strlen(line)-1]=NUL;
-		(void) fputs("\\parpic[r][rt]{\\includegraphics[width=3in,keepaspectratio]{",b);
+		(void) fputs("\\begin{figure}[htb]\n\\centering\\includegraphics[width=3in,keepaspectratio]{",b);
 		fputs(line+1, b);
-		(void) fputs("}}\n",b);
+		(void) fputs("}\n\\end{figure}\n",b);
 	    }
 	    break;