Don't list platform-posix.cc twice on android

BUG=387326
R=marja@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/350893002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21967 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

BUILD.gn

@@ -986,7 +986,6 @@ source_set("v8_base") {
     }
   } else if (is_android) {
     defines += [ "CAN_USE_VFP_INSTRUCTIONS" ]
-    sources += [ "src/platform-posix.cc" ]
 
     if (build_os == "mac") {
       if (current_toolchain == host_toolchain) {