Disable -Wl,-z,defs on mipsel to suppress ffmpeg error

The ffmpeg build on mips is broken which manifests in build errors when
z,defs is specified. The owners of this build would like the compile
time error to be suppressed for now while they work on a proper fix.

BUG=450771,371125

Review URL: https://codereview.chromium.org/864193002

Cr-Commit-Position: refs/heads/master@{#312557}

build/config/compiler/BUILD.gn

@@ -350,7 +350,10 @@ config("compiler") {
       "-Wl,-z,now",
       "-Wl,-z,relro",
     ]
-    if (!using_sanitizer) {
+
+    # TODO(zork): The mipsel build is broken in ffmpeg, guard this flag for now
+    # to hide the breakage. https://crbug.com/450771
+    if (!using_sanitizer && cpu_arch != "mipsel") {
       ldflags += [ "-Wl,-z,defs" ]
     }
   }