*: fix builds by disregarding warning from new glibc

Also, in case of collectd, the -lgcc_s shouldn't be needed anymore,
as the library is in ${glibc}/lib/ now, which is practically always on RPATH.

In case of seyren it was some stdenv change uncovering the mistake of
putting src into buildInputs.

pkgs/tools/system/collectd/default.nix

@@ -33,8 +33,6 @@ stdenv.mkDerivation rec {
     sha256 = "1q365zx6d1wyhv7n97bagfxqnqbhj2j14zz552nhmjviy8lj2ibm";
   };
 
-  NIX_LDFLAGS = "-lgcc_s"; # for pthread_cancel
-
   buildInputs = [
     pkgconfig curl iptables libcredis libdbi libgcrypt libmemcached cyrus_sasl
     libmodbus libnotify gdk_pixbuf liboping libpcap libsigrok libvirt
@@ -45,6 +43,8 @@ stdenv.mkDerivation rec {
   # for some reason libsigrok isn't auto-detected
   configureFlags = stdenv.lib.optional (libsigrok != null) "--with-libsigrok";
 
+  NIX_CFLAGS_COMPILE = "-Wno-error=cpp";
+
   meta = with stdenv.lib; {
     description = "Daemon which collects system performance statistics periodically";
     homepage = http://collectd.org;