kconfig: if ncurses-devel is missing then say so

With this patch when ncurses-devel (or whatever it is named)
is missing trying to run menuconfig will result in this:

$ make menuconfig
HOSTCC scripts/kconfig/conf.o
HOSTCC scripts/kconfig/kxgettext.o
*** Unable to find the ncurses libraries or the
*** required header files.
*** 'make menuconfig' requires the ncurses libraries.
***
*** Install ncurses (ncurses-devel) and try again.
***
make[1]: *** [scripts/kconfig/dochecklxdialog] Error 1
make: *** [menuconfig] Error 2

Much better than before where we just listed some build errors.
The other *config targets will work indepenednt on ncurses
being present or not.

Includes improvements suggested by: Frans Pop <[e-mail]>

Signed-off-by: Sam Ravnborg <[e-mail]>
Cc: Frans Pop <[e-mail]>

scripts/kconfig/Makefile

···
 
 HOST_EXTRACFLAGS += -DLOCALE
 
-PHONY += $(obj)/dochecklxdialog
-$(obj)/dochecklxdialog:
-	$(Q)$(CONFIG_SHELL) $(check-lxdialog) -check $(HOSTCC) $(HOST_LOADLIBES)
-
-always := dochecklxdialog
-
 
 # ===========================================================================
 # Shared Makefile for the various kconfig executables:
···
 clean-files	:= lkc_defs.h qconf.moc .tmp_qtcheck \
 		   .tmp_gtkcheck zconf.tab.c lex.zconf.c zconf.hash.c
 clean-files     += mconf qconf gconf
+
+# Check that we have the required ncurses stuff installed for lxdialog (menuconfig)
+PHONY += $(obj)/dochecklxdialog
+$(addprefix $(obj)/,$(lxdialog)): $(obj)/dochecklxdialog
+$(obj)/dochecklxdialog:
+	$(Q)$(CONFIG_SHELL) $(check-lxdialog) -check $(HOSTCC) $(HOST_EXTRACFLAGS) $(HOST_LOADLIBES)
+
+always := dochecklxdialog
 
 # Add environment specific flags
 HOST_EXTRACFLAGS += $(shell $(CONFIG_SHELL) $(srctree)/$(src)/check.sh $(HOSTCC) $(HOSTCFLAGS))

scripts/kconfig/lxdialog/check-lxdialog.sh

···
 
 # Check if we can link to ncurses
 check() {
-	echo "main() {}" | $cc -xc - -o $tmp 2> /dev/null
+	echo -e " #include CURSES_LOC \n main() {}" |
+	    $cc -xc - -o $tmp 2> /dev/null
 	if [ $? != 0 ]; then
-		echo " *** Unable to find the ncurses libraries."          1>&2
-		echo " *** make menuconfig require the ncurses libraries"  1>&2
-		echo " *** "                                               1>&2
-		echo " *** Install ncurses (ncurses-devel) and try again"  1>&2
-		echo " *** "                                               1>&2
-		exit 1
+	    echo " *** Unable to find the ncurses libraries or the"       1>&2
+	    echo " *** required header files."                            1>&2
+	    echo " *** 'make menuconfig' requires the ncurses libraries." 1>&2
+	    echo " *** "                                                  1>&2
+	    echo " *** Install ncurses (ncurses-devel) and try again."    1>&2
+	    echo " *** "                                                  1>&2
+	    exit 1
 	fi
 }