Update and improve android_gradle (#965)

* Update CMakeLists.txt files so we can build libamber_ndk.so for
Android via CMake.

* `android_gradle/`:

  * Update Gradle version, settings, and build files to match the latest
  Android sample. Importantly, this removes the use of jcenter and
  bintray repositories, which were shut down.

  * Specify NDK version so that Gradle can install required native build
  tools automatically.

  * Define externalNativeBuild so Gradle can perform the Android CMake
  build automatically.

* Replace `main` with `android_main` when building the Amber tool as a
library for Android to avoid compiler warnings, and rename other
Android-related symbols to avoid confusion.

Fixes #964

1 files changed, 8 insertions, 0 deletions

diff --git a/samples/amber.cc b/samples/amber.cc
index d037ba4..5973dba 100644
--- a/samples/amber.cc
+++ b/samples/amber.cc
@@ -447,7 +447,15 @@ std::string disassemble(const std::string& env,
 
 }  // namespace
 
+#ifdef AMBER_ANDROID_MAIN
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wmissing-prototypes"
+#pragma ide diagnostic ignored "OCUnusedGlobalDeclarationInspection"
+int android_main(int argc, const char** argv) {
+#pragma clang diagnostic pop
+#else
 int main(int argc, const char** argv) {
+#endif
   std::vector<std::string> args(argv, argv + argc);
   Options options;
   SampleDelegate delegate;