[BUILD] Add "-lm" linker flags, which are needed on certain platforms.

This change was suggested in #12; this commit formats the change slightly differently.

PiperOrigin-RevId: 142557801

BUILD

@@ -537,7 +537,10 @@ cc_binary(
         "-DQDECL=",
         "-pthread",
     ],
-    linkopts = ["-pthread"],
+    linkopts = [
+        "-pthread",
+        "-lm",
+    ],
     visibility = ["//deepmind/level_generation:__subpackages__"],
     deps = ["@zlib_archive//:zlib"],
 )
@@ -908,7 +911,10 @@ cc_binary(
         ":non_pk3_assets",
         ":vm_pk3",
     ],
-    linkopts = ["-lGL"],
+    linkopts = [
+        "-lGL",
+        "-lm",
+    ],
     deps = [
         ":game_lib_sdl",
         "//deepmind/engine:callbacks",