do not hardcode /usr/include paths

--- a/configure.ac
+++ b/configure.ac
@@ -668,6 +668,8 @@ AC_ARG_WITH(cxx_main,
 ])
 AC_MSG_RESULT($with_cxx_main)
 
+AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
+
 preset_cxx="$CXX"
 if test -z "$CXX"
 then
@@ -1513,7 +1515,7 @@ dnl AC_MSG_RESULT($cpp_type)
 # checks for header files
 AC_HEADER_STDC
 ac_save_cppflags="$CPPFLAGS"
-CPPFLAGS="$CPPFLAGS -I/usr/include/ncursesw"
+CPPFLAGS="$CPPFLAGS `$PKG_CONFIG --cflags ncursesw`"
 AC_CHECK_HEADERS(asm/types.h conio.h curses.h direct.h dlfcn.h errno.h \
 fcntl.h grp.h \
 ieeefp.h io.h langinfo.h libintl.h ncurses.h process.h pthread.h \
@@ -2225,8 +2227,6 @@ LIBS="$withval $LIBS"
 ],
 [AC_MSG_RESULT(no)])
 
-AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
-
 # Check for use of the system expat library
 AC_MSG_CHECKING(for --with-system-expat)
 AC_ARG_WITH(system_expat,
@@ -4273,7 +4273,7 @@ then
 fi
 
 ac_save_cppflags="$CPPFLAGS"
-CPPFLAGS="$CPPFLAGS -I/usr/include/ncursesw"
+CPPFLAGS="$CPPFLAGS `$PKG_CONFIG --cflags ncursesw`"
 # On HP/UX 11.0, mvwdelch is a block with a return statement
 AC_MSG_CHECKING(whether mvwdelch is an expression)
 AC_CACHE_VAL(ac_cv_mvwdelch_is_expression,