perf: polkit is optional for the library

So changing this was a little backwards. The goal here is to allow using
libsysprof-2 without polkit, it just won't have the ability to elevate
privileges.

lib/Makefile.am

@@ -99,7 +99,6 @@ libsysprof_@API_VERSION@_la_SOURCES = \
 libsysprof_@API_VERSION@_la_CFLAGS = \
 	-I$(srcdir)/util \
 	$(GIO_CFLAGS) \
-	$(POLKIT_CFLAGS) \
 	$(WARN_CFLAGS) \
 	$(NULL)
 
@@ -107,7 +106,6 @@ libsysprof_@API_VERSION@_la_LIBADD = \
 	libutil.la \
 	-lstdc++ \
 	$(GIO_LIBS) \
-	$(POLKIT_LIBS) \
 	$(NULL)
 
 if ENABLE_SYSPROFD

lib/sp-perf-counter.c

@@ -42,13 +42,16 @@
 #include <errno.h>
 #include <gio/gio.h>
 #include <gio/gunixfdlist.h>
-#include <polkit/polkit.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
+#ifdef ENABLE_SYSPROFD
+# include <polkit/polkit.h>
+#endif
+
 #include "sp-perf-counter.h"
 
 #include "util.h"