android: Enable build against API level 21

While building against this level in general would break our app on
older systems, the NDK will automatically use this level for 64-bit
ABI builds (which are not supported in older levels).  So to build
against 64-bit ABIs we have to support this API level.

Android.mk

@@ -61,7 +61,6 @@ strongswan_CFLAGS := \
 	-DHAVE_ALLOCA \
 	-DHAVE_CLOCK_GETTIME \
 	-DHAVE_DLADDR \
-	-DHAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC \
 	-DHAVE_PRCTL \
 	-DHAVE_LINUX_UDP_H \
 	-DHAVE_STRUCT_SADB_X_POLICY_SADB_X_POLICY_PRIORITY \

src/frontends/android/app/src/main/jni/Android.mk

@@ -39,7 +39,6 @@ strongswan_CFLAGS := \
 	-DHAVE_ALLOCA \
 	-DHAVE_CLOCK_GETTIME \
 	-DHAVE_DLADDR \
-	-DHAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC \
 	-DHAVE_PRCTL \
 	-DHAVE_LINUX_UDP_H \
 	-DHAVE_STRUCT_SADB_X_POLICY_SADB_X_POLICY_PRIORITY \

src/libstrongswan/utils/compat/android.h

@@ -21,6 +21,8 @@
 #ifndef ANDROID_H_
 #define ANDROID_H_
 
+#include <android/api-level.h>
+
 /* stuff defined in AndroidConfig.h, which is included using the -include
  * command-line option, thus cannot be undefined using -U CFLAGS options.
  * the reason we have to undefine these flags in the first place, is that
@@ -28,4 +30,19 @@
  * actually defined. */
 #undef HAVE_BACKTRACE
 
+/* API level 21 changed quite a few things, we define some stuff here and not
+ * via CFLAGS in Android.mk files as it is easier to compare versions */
+#if __ANDROID_API__ >= 21
+
+#define HAVE_PTHREAD_CONDATTR_INIT 1
+#define HAVE_CONDATTR_CLOCK_MONOTONIC 1
+
+#define HAVE_SYS_CAPABILITY_H 1
+
+#else /* __ANDROID_API__ */
+
+#define HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC 1
+
+#endif /* __ANDROID_API__ */
+
 #endif /** ANDROID_H_ @}*/