Backport: * configure.ac (HAVE_XPM): Explain the use of CPPFLAGS in the...

Backport: * configure.ac (HAVE_XPM): Explain the use of CPPFLAGS in the Cygwin-w32 build.  (Bug#18302)

ChangeLog

+2014-08-22  Ken Brown  <kbrown@cornell.edu>
+
+	* configure.ac (HAVE_XPM): Explain the use of CPPFLAGS in the
+	Cygwin-w32 build.  (Bug#18302)
+
 2014-08-10  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Don't prevent random file systems from being unmounted (Bug#18232).

configure.ac

@@ -2969,6 +2969,9 @@ AC_SUBST(M17N_FLT_LIBS)
 
 ### Use -lXpm if available, unless `--with-xpm=no'.
 ### mingw32 doesn't use -lXpm, since it loads the library dynamically.
+### In the Cygwin-w32 build, we need to use /usr/include/noX/X11/xpm.h
+### rather than /usr/include/X11/xpm.h, so we set CPPFLAGS (and
+### LDFLAGS) accordingly.
 HAVE_XPM=no
 LIBXPM=
 if test "${HAVE_W32}" = "yes" && test "${opsys}" = "cygwin"; then