Enhance build process (#994)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/994

After building yoga aar, we found several issues:
1. More dynamic so files. This is bad as lower-end Android devices cannot load that many sos.
2. Size increase.
3. (Minor) The libs are stored in asset folder rather than "libs/".

We apply the following optimizations:
1. Remove dependency on memalign16 (this is brought in by a pure header dependency jni-hack);
2. Enable native relinker to remove unused symbols in the so files.
3. Link yogacore statically to reduce size churn.

Reviewed By: SidharthGuglani

Differential Revision: D20808623

fbshipit-source-id: 6c6bbd4f71b6bf6ad272ec05dd56696ddb14a8e0

BUCK

@@ -40,6 +40,20 @@ yoga_cxx_library(
     ],
 )
 
+yoga_cxx_library(
+    name = "yoga-static",
+    srcs = glob(["yoga/**/*.cpp"]),
+    compiler_flags = LIBRARY_COMPILER_FLAGS,
+    preferred_linkage = "static",
+    public_include_directories = ["."],
+    raw_headers = glob(["yoga/**/*.h"]),
+    tests = [":YogaTests"],
+    visibility = ["PUBLIC"],
+    deps = [
+        ":ndklog",
+    ],
+)
+
 yoga_cxx_library(
     name = "yogaForDebug",
     srcs = glob(["yoga/**/*.cpp"]),