*: 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/os-specific/linux/disk-indicator/default.nix

@@ -18,6 +18,8 @@ stdenv.mkDerivation {
 
   buildPhase = "make -f makefile";
 
+  NIX_CFLAGS_COMPILE = "-Wno-error=cpp";
+
   installPhase = ''
     mkdir -p "$out/bin"
     cp ./disk_indicator "$out/bin/"