Fix gcc 5.x build failure

Extracted from upstream commit
http://ncurses.scripts.mit.edu/?p=ncurses.git;a=commit;h=97bb4678dc03e753290b39bbff30ba2825df9517.

+ modify MKlib_gen.sh to work around change in development version of
  gcc introduced here:
  https://gcc.gnu.org/ml/gcc-patches/2014-06/msg02185.html
  https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00236.html
  (reports by Marcus Shawcroft, Maohui Lei).

Original author: Thomas E. Dickey <dickey@invisible-island.net>
Signed-off-by: Mikhail Peselnik <bas@bmail.ru>

--- a/ncurses/base/MKlib_gen.sh 2015-08-06 20:48:24.000000000 -0400
+++ b/ncurses/base/MKlib_gen.sh	2017-02-07 10:09:01.293962392 -0500
@@ -491,11 +491,22 @@
 	-e 's/gen_$//' \
 	-e 's/  / /g' >>$TMP
 
+cat >$ED1 <<EOF
+s/  / /g
+s/^ //
+s/ $//
+s/P_NCURSES_BOOL/NCURSES_BOOL/g
+EOF
+
+# A patch discussed here:
+#       https://gcc.gnu.org/ml/gcc-patches/2014-06/msg02185.html
+# introduces spurious #line markers.  Work around that by ignoring the system's
+# attempt to define "bool" and using our own symbol here.
+sed -e 's/bool/P_NCURSES_BOOL/g' $TMP > $ED2
+cat $ED2 >$TMP
+
 $preprocessor $TMP 2>/dev/null \
-| sed \
-	-e 's/  / /g' \
-	-e 's/^ //' \
-	-e 's/_Bool/NCURSES_BOOL/g' \
+| sed -f $ED1 \
 | $AWK -f $AW2 \
 | sed -f $ED3 \
 | sed \