attempt to fix dynamic library build error

```
/nix/store/mzrw2zphz9xx9s3qq8x5zpf18isp0jga-go-1.20.3/share/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/nix/store/ybw485608d7f1yv1v071j2052q64mvla-binutils-2.40/bin/ld: /build/go-link-2631521468/go.o: relocation R_X86_64_TPOFF32 against `runtime.tlsg' can not be used when making a shared object; recompile with -fPIC
/nix/store/ybw485608d7f1yv1v071j2052q64mvla-binutils-2.40/bin/ld: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status
```

Signed-off-by: Jakub Sokołowski <jakub@status.im>

default.nix

@@ -3,6 +3,7 @@
   self ? ./.,
   subPkgs ? "cmd/waku",
   ldflags ? [],
+  cgoLdflags ? "",
   output ? null,
   commit ? builtins.substring 0 7 (self.rev or "dirty"),
   version ? builtins.readFile ./VERSION,
@@ -18,6 +19,8 @@ pkgs.buildGo120Module {
     "-X github.com/waku-org/go-waku/waku/v2/node.GitCommit=${commit}"
     "-X github.com/waku-org/go-waku/waku/v2/node.Version=${version}"
   ] ++ ldflags;
+  CGO_LDFLAGS = cgoLdflags;
+  GOGCCFLAGS = "-fPIC";
   doCheck = false;
 
   # Otherwise library would be just called bin/c.

flake.nix

@@ -53,7 +53,8 @@
           inherit self;
           subPkgs = ["library/c"];
           ldflags = ["-buildmode=c-shared"];
-          output = "libgowaku.a";
+          cgoLdflags = "-Wl,-Bsymbolic,-soname,libgowaku.so.0";
+          output = "libgowaku.so";
         };
       });