Use the appropiate MAKEINFO variable rather than the hardcoded makeinfo
command directly, otherwise missing logic never works.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura bc-1.06.95.orig/doc/Makefile.in bc-1.06.95/doc/Makefile.in
--- bc-1.06.95.orig/doc/Makefile.in	2015-06-13 09:39:46.946620294 -0300
+++ bc-1.06.95/doc/Makefile.in	2015-06-13 09:40:10.019407630 -0300
@@ -96,7 +96,7 @@
 LIBOBJS = @LIBOBJS@
 LIBS = @LIBS@
 LTLIBOBJS = @LTLIBOBJS@
-MAKEINFO = makeinfo --no-split
+MAKEINFO = @MAKEINFO@ --no-split
 OBJEXT = @OBJEXT@
 PACKAGE = @PACKAGE@
 PACKAGE_BUGREPORT = @PACKAGE_BUGREPORT@
