Probably a missing dependency:

  CXX     output/ANDROID/./src/Android/InternalGPS.o
src/Android/InternalGPS.cpp:27:36: error: org_xcsoar_InternalGPS.h: No such file or directory
  CXX     output/ANDROID/./src/Android/SoundUtil.o
  CXX     output/ANDROID/./src/Android/TextUtil.o
  CXX     output/ANDROID/./src/Android/Timer.o
  CXX     output/ANDROID/./src/Android/EventBridge.o
src/Android/Timer.cpp:30:30: error: org_xcsoar_Timer.h: No such file or directory
src/Android/EventBridge.cpp:24:36: error: org_xcsoar_EventBridge.h: No such file or directory
cc1plus: warnings being treated as errors
src/Android/Timer.cpp: In function 'void Java_org_xcsoar_Timer_run(JNIEnv*, _jobject*, jlong)':
src/Android/Timer.cpp:92: error: no previous declaration for 'void Java_org_xcsoar_Timer_run(JNIEnv*, _jobject*, jlong)'

Workaround: build missing files manually:

make TARGET=ANDROID output/ANDROID/include/org_xcsoar_InternalGPS.h 
output/ANDROID/include/org_xcsoar_Timer.h 
output/ANDROID/include/org_xcsoar_NativeView.h 
output/ANDROID/include/org_xcsoar_EventBridge.h