Add target to build symupload & dump_syms for iOS.

The symupload and dump_syms tools are required as part of the official
build on iOS. They are build and run on the host as part of the build.

BUG=634777

Review-Url: https://codereview.chromium.org/2220163002
Cr-Commit-Position: refs/heads/master@{#410256}

breakpad/BUILD.gn

@@ -332,6 +332,15 @@ if (is_mac) {
   }
 }
 
+if (is_ios) {
+  binary_symlink("dump_syms") {
+    binary_label = ":$target_name($host_toolchain)"
+  }
+  binary_symlink("symupload") {
+    binary_label = ":$target_name($host_toolchain)"
+  }
+}
+
 if (is_mac) {
   static_library("utilities") {
     sources = [