' __exidx_start' and '__exidx_end' what do they do?

These symbols are used internally by call-chain unwinding mechanism in GCC that takes control during exception handling phase. For instance, there is an example in unwind-arm-common.inc:104 where the boundaries of exception-handling table are obtained as pointers to these symbols.

As for .ARM.exidx*-entries that the symbols enclose, they form an exception-handling index table, which is a part of ARM Exception Handling ABI (in sect. 4.4.1) for C++.

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Update 20.05.2020

Answering the question by @pixelou:
These sections are not related to debugging, but form a basis of exception unwinding mechanism. Stripping the the *.exidx* sections causes disability to clean the mess up forcing program to abort (fail completly) instead of accurate handling of invalid states on stack. Without that unwinding information a program behaves like if it's built with -fno-exceptions option.