Add support for x86_64 builds (#128)

Summary:
Add the required compiler flag for Folly when building x86_64.

I'll prepare a new release for this shortly.

Depends on #126
Closes https://github.com/facebook/Sonar/pull/128

Reviewed By: danielbuechele

Differential Revision: D8731955

Pulled By: priteshrnandgaonkar

fbshipit-source-id: 9511811b0b51205989a5200ad9d0d8689ca684cb

android/build.gradle

@@ -211,7 +211,7 @@ android {
         buildConfigField "boolean", "IS_INTERNAL_BUILD", 'true'
 
         ndk {
-            abiFilters 'x86', 'armeabi-v7a', 'arm64-v8a'
+            abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
         }
 
         externalNativeBuild {