make prepareGlog idempotent

Summary:
The path to copy log_severity.h could refer to the
destination, which would result in an empty file being copied on some
rebuilds.

Reviewed By: willholen

Differential Revision: D15018283

fbshipit-source-id: 0081526a9686de8c74753738c165753de6dda18d

ReactAndroid/build.gradle

@@ -126,7 +126,7 @@ task prepareGlog(dependsOn: dependenciesPath ? [] : [downloadGlog], type: Copy)
 
     doLast {
         copy {
-            from(fileTree(dir: "$thirdPartyNdkDir/glog", includes: ["stl_logging.h", "logging.h", "raw_logging.h", "vlog_is_on.h", "**/glog/log_severity.h"]).files)
+            from(fileTree(dir: "$thirdPartyNdkDir/glog", includes: ["stl_logging.h", "logging.h", "raw_logging.h", "vlog_is_on.h", "**/src/glog/log_severity.h"]).files)
             includeEmptyDirs = false
             into("$thirdPartyNdkDir/glog/exported/glog")
         }