Support !-style fast calls for Android
Summary:
Adds support for `!`-style fast calls in Android versions < 8.
For now, this comes with the following restrictions:
- has to be enabled with a macro
- only supports native functions that return and accept primitive Java types (`jint`, `jdouble`, etc.), and `void`
- this is supposed to map to `CriticalNative` as described in https://source.android.com/devices/tech/dalvik/improvements#faster-native-methods.
Inline documentation in art: http://androidxref.com/6.0.1_r10/xref/art/runtime/jni_internal.cc#2110
Possible follow ups:
- don’t prefix when the Android runtime is too new (to avoid the warning, and future error, see http://androidxref.com/8.1.0_r33/xref/art/runtime/jni_internal.cc#2355)
- shim `CriticalNative` (see https://android.googlesource.com/platform/libcore/+/master/dalvik/src/main/java/dalvik/annotation/optimization/CriticalNative.java)
- test whether we can use `CriticalNative` at all (docs claim classes must be on bootclasspath)
- suppport `FastNative`, i.e. instance methods that can also receive and return `jobject`
Reviewed By: cjhopman
Differential Revision: D9630538
fbshipit-source-id: 0ae86c909b192429d60f8eddb15528cc38610379
328ec7dc4d