Fix static linking with libsystemd

libsystemd requires libcap for static linking.

Add missing macro for function alias.
diff --git a/configure.ac b/configure.ac
index fe7f7b3..8de3c1d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -336,7 +336,7 @@
 fi
 
 if test "$my_htop_platform" = linux && test "x$enable_static" = xyes; then
-   AC_CHECK_LIB([systemd], [sd_bus_open_system])
+   AC_CHECK_LIB([systemd], [sd_bus_open_system], [], [], [-lcap])
 fi
 
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