Link to the OpenGL library to fix the host_debug_unopt build (#2841)

sky/shell/BUILD.gn

@@ -402,6 +402,10 @@ if (is_android) {
       ":testing",
     ]
 
+    ldflags = [
+      "-lGL",
+    ]
+
     if (use_glfw) {
       sources += [
         "//sky/shell/platform/glfw/init_glfw.cc",

sky/shell/platform/mojo/BUILD.gn

@@ -47,4 +47,8 @@ mojo_native_application("mojo") {
     "//sky/shell:gpu_mojo",
     "//third_party/icu",
   ]
+
+  ldflags = [
+    "-lGL",
+  ]
 }