[gdb/testsuite] share jit-protocol.h by all jit tests

[gdb/testsuite] share jit-protocol.h by all jit tests

There was an existing jit-protocol.h defining common symbols needed for
JIT-supporting application, however, it was only used by few tests.
Others redeclared the same symbols.

This unifies all tests to use jit-protocol.h

gdb/testsuite/ChangeLog:

2020-02-18  Mihails Strasuns  <mihails.strasuns@intel.com>

	* gdb.base/jit-attach-pie.c: Use jit-protocol.h.
	* gdb.base/jit-elf-main.c: Use jit-protocol.h.
	* gdb.base/jit-reader-host.c: Use jit-protocol.h.
	* gdb.base/jit-reader-simple-jit.c: Use jit-protocol.h.
	* gdb.base/jit-protocol.h: Update definitions to match all usage
	  contexts.