Begone buckBuildAndCopy!

Summary:
I'm actually quite excited about this one!

No more buck shelling out for building the Yoga AARs/JARs via Gradle. It's now
all done via Gradle.

This commit is the only one that should actually change anything about the entry
points to the gradle builds and release process. **So if anything goes wrong
with the next release, reverting this one here should be enough!**

Reviewed By: emilsjolander

Differential Revision: D4913600

fbshipit-source-id: 4a54562ad5be69f62a7781d43fddad211f99ab25

java/build.gradle

@@ -6,12 +6,6 @@ apply plugin: 'maven-publish'
 version = '1.4.2'
 group = 'com.facebook.yoga'
 
-// We currently build the native libraries with buck and bundle them together
-// at this point into the AAR
-task buckBuildAndCopy(type: Exec) {
-    commandLine "$rootDir/scripts/build_natives_for_gradle.sh"
-}
-
 android {
     compileSdkVersion rootProject.compileSdkVersion
     buildToolsVersion rootProject.buildToolsVersion
@@ -19,6 +13,22 @@ android {
     defaultConfig {
         minSdkVersion rootProject.minSdkVersion
         targetSdkVersion rootProject.targetSdkVersion
+
+        ndk {
+            abiFilters 'x86', 'x86_64', 'armeabi', 'armeabi-v7a', 'arm64-v8a'
+        }
+
+        externalNativeBuild {
+            cmake {
+                arguments '-DANDROID_TOOLCHAIN=clang', '-DANDROID_STL=c++_static'
+            }
+        }
+    }
+
+    externalNativeBuild {
+        cmake {
+            path 'CMakeLists.txt'
+        }
     }
 
     compileOptions {
@@ -36,8 +46,6 @@ android {
     }
 }
 
-preBuild.dependsOn buckBuildAndCopy
-
 dependencies {
     compile 'com.google.code.findbugs:jsr305:3.0.1'
     compile 'com.facebook.soloader:soloader:0.2.0'