*: 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/servers/sql/mariadb/default.nix

@@ -17,6 +17,8 @@ stdenv.mkDerivation rec {
 
   cmakeFlags = [ "-DWITH_READLINE=yes" "-DWITH_EMBEDDED_SERVER=yes" "-DINSTALL_SCRIPTDIR=bin" ];
 
+  NIX_CFLAGS_COMPILE = "-Wno-error=cpp";
+
   enableParallelBuilding = true;
 
   prePatch = ''