Link against -lcap only where required

Don't put -lcap into LIBS as otherwise everything will be linked against
it, like libsystemd-daemon, where this is not desired.

Makefile.am

@@ -545,7 +545,8 @@ libsystemd_basic_la_CFLAGS = \
 	$(SELINUX_CFLAGS)
 
 libsystemd_basic_la_LIBADD = \
-	$(SELINUX_LIBS)
+	$(SELINUX_LIBS) \
+	$(CAP_LIBS)
 
 libsystemd_core_la_SOURCES = \
 	src/unit.c \
@@ -614,7 +615,8 @@ libsystemd_core_la_LIBADD = \
 	$(UDEV_LIBS) \
 	$(LIBWRAP_LIBS) \
 	$(PAM_LIBS) \
-	$(AUDIT_LIBS)
+	$(AUDIT_LIBS) \
+	$(CAP_LIBS)
 
 # This is needed because automake is buggy in how it generates the
 # rules for C programs, but not Vala programs.  We therefore can't

configure.ac

@@ -111,8 +111,14 @@ LT_INIT
 
 AC_SEARCH_LIBS([clock_gettime], [rt], [], [AC_MSG_ERROR([*** POSIX RT library not found])])
 AC_SEARCH_LIBS([dlsym], [dl], [], [AC_MSG_ERROR([*** Dynamic linking loader library not found])])
+
+save_LIBS="$LIBS"
+LIBS=
 AC_SEARCH_LIBS([cap_init], [cap], [], [AC_MSG_ERROR([*** POSIX caps library not found])])
 AC_CHECK_HEADERS([sys/capability.h], [], [AC_MSG_ERROR([*** POSIX caps headers not found])])
+CAP_LIBS="$LIBS"
+LIBS="$save_LIBS"
+AC_SUBST(CAP_LIBS)
 
 # This makes sure pkg.m4 is available.
 m4_pattern_forbid([^_?PKG_[A-Z_]+$],[*** pkg.m4 missing, please install pkg-config])