uim: pull upstream fix for -fno-common toolchains

Without the change build fails on upstream gcc-10 as:

    ld: .libs/mach_dep.o:sigscheme/libgcroots/include/private/gc_priv.h:2029: multiple definition of
      `GCROOTS_jmp_buf'; .libs/mark.o:sigscheme/libgcroots/include/private/gc_priv.h:2029: first defined here

pkgs/tools/inputmethods/uim/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub, shared-mime-info
+{ lib, stdenv, fetchFromGitHub, fetchpatch, shared-mime-info
 , autoconf, automake, intltool, libtool, pkg-config, cmake
 , ruby, librsvg
 , ncurses, m17n_lib, m17n_db, expat
@@ -86,7 +86,21 @@ stdenv.mkDerivation rec {
     ./autogen.sh
   '';
 
-  patches = [ ./data-hook.patch ];
+  patches = [
+    ./data-hook.patch
+
+    # Pull upstream fix for -fno-common toolchains
+    #   https://github.com/uim/libgcroots/pull/4
+    (fetchpatch {
+      name = "libgcroots-fno-common.patch";
+      url = "https://github.com/uim/libgcroots/commit/7e39241344ad0663409e836560ae6b5eb231e1fc.patch";
+      sha256 = "0iifcl5lk8bvl0cflm47gkymg88aiwzj0gxh2aj3mqlyhvyx78nz";
+      # Patch comes from git submodule. Relocate as:
+      # a/include/private/gc_priv.h -> a/sigscheme/libgcroots/include/private/gc_priv.h
+      stripLen = 1;
+      extraPrefix = "sigscheme/libgcroots/";
+    })
+  ];
 
   configureFlags = [
     # configure in maintainer mode or else some pixmaps won't get autogenerated