do not remove version sections

remove DT_FLAGS_1=0x8 if built for API less than 23

Better compatibility with Android 5.

do not remove GNU version sections when API is >= 23

remove DT_GNU_HASH if targeted at Android API 21 (or lower)

support for Android 7

Remove DT_VERSYM, DT_VERNEEDED, DT_VERNEEDNUM, DT_VERDEF,
DT_VERDEFNUM only on Android 5.

Keep DT_RUNPATH on Android 7 and higher.

Keep DF_1_NODELETE as DT_FLAGS_1 value

Android started supporting DF_1_NODELETE in 6.0 - older versions
can keep warning about it.

Update makefile