rework pam, ncurses and termcap include files

This allows error checking inside the included files instead of either
including the appropriate file or a blank file.

Also the blank file named .mk gets removed by this change.

mk/ncurses.mk

@@ -1,3 +0,0 @@
-LIBTERMCAP?=	-lncurses
-CPPFLAGS+=	-DHAVE_TERMCAP
-LDADD+=		${LIBTERMCAP}

mk/pam.mk

@@ -1,6 +1,10 @@
+ifeq (${MKPAM},pam)
 LIBPAM?=	-lpam
 CPPFLAGS+=	-DHAVE_PAM
 LDADD+=		${LIBPAM}
 
 PAMDIR?=	/etc/pam.d
 PAMMODE?=	0644
+else ifneq (${MKPAM},)
+$(error if MKPAM is defined, it must be "pam")
+endif

mk/termcap.mk

@@ -1,3 +1,11 @@
+ifeq (${MKTERMCAP},ncurses)
+LIBTERMCAP?=	-lncurses
+CPPFLAGS+=	-DHAVE_TERMCAP
+LDADD+=		${LIBTERMCAP}
+else ifeq (${MKTERMCAP},termcap)
 LIBTERMCAP?=	-ltermcap
 CPPFLAGS+=	-DHAVE_TERMCAP
 LDADD+=		${LIBTERMCAP}
+else ifneq (${MKTERMCAP},)
+$(error If MKTERMCAP is defined, it must be ncurses or termcap)
+endif

src/libeinfo/Makefile

@@ -10,4 +10,4 @@ MK=			../../mk
 include ${MK}/lib.mk
 include ${MK}/cc.mk
 include ${MK}/debug.mk
-include ${MK}/${MKTERMCAP}.mk
+include ${MK}/termcap.mk

src/rc/Makefile

@@ -41,9 +41,9 @@ include ${MK}/prog.mk
 include ${MK}/git.mk
 include ${MK}/cc.mk
 
-include ${MK}/${MKTERMCAP}.mk
+include ${MK}/termcap.mk
 LDADD+=		${LIBDL} ${LIBKVM}
-include ${MK}/${MKPAM}.mk
+include ${MK}/pam.mk
 
 # create symlinks to rc if not an SELINUX system, otherwise create a wrapper
 # script to call rc with the proper name of the applet to execute.