Provide support for API 16+ (#37)

But don't change `minSDKVersion` yet. We need to have internal discussion about the impacts to releases and client-side unwinding support.

Author: rqbacktrace

README.md

@@ -72,7 +72,7 @@ catch (e: Exception) {
 * Supports Breadcrumbs.
 
 # Supported SDKs <a name="supported-sdks"></a>
-* Minimum SDK version 21 (Android 5.0)
+* Minimum SDK version 16 (Android 4.1.x)
 * Target SDK version 30 (Android 11.0)
 * Minimum NDK version 16b
 * Maximum NDK version 22
@@ -561,6 +561,8 @@ database.setupNativeIntegration(backtraceClient, credentials, true);
 
 **NOTE:** Client side unwinding is only available in NDK level 17+ (i.e: Only with the Crashpad crash reporting backend)
 
+**NOTE:** Client side unwinding is only available in SDK level 21+ (i.e: If minSDKVersion < 21, client-side unwinding will be disabled for 32-bit arm platforms)
+
 ### Unwinding Modes and Options
 
 You can optionally specify the unwinding mode (`REMOTE_DUMPWITHOUTCRASH` is the default)

backtrace-library/src/main/cpp/CMakeLists.txt

@@ -16,6 +16,13 @@ elseif (NOT ANDROID_NDK_MAJOR)
     set(BACKEND "BREAKPAD_BACKEND")
 elseif(ANDROID_NDK_MAJOR LESS 17)
     set(BACKEND "BREAKPAD_BACKEND")
+elseif(ANDROID_NATIVE_API_LEVEL LESS 21)
+    set(BACKEND "CRASHPAD_BACKEND")
+    # 64 bit architectures will always have min API level 21
+    # https://stackoverflow.com/a/56467008
+    if (NOT ANDROID_ABI STREQUAL "armeabi-v7a")
+        set(CLIENT_SIDE_UNWINDING TRUE)
+    endif()
 else()
     set(BACKEND "CRASHPAD_BACKEND")
     set(CLIENT_SIDE_UNWINDING TRUE)