gdb/reverse: Fix continue_to_breakpoint in syscall testcases.

gdb/reverse: Fix continue_to_breakpoint in syscall testcases.

continue_to_breakpoint always continues to the next breakpoint, not to the
one named in parameter.  This rendered the tests effectively useless, since
marker2 was never reached.

gdb/testsuite/ChangeLog:

	* gdb.reverse/fstatat-reverse.exp: Set breakpoint on marker1 after
	reaching marker2.
	* gdb.reverse/getresuid-reverse.exp: Likewise.
	* gdb.reverse/pipe-reverse.exp: Likewise.
	* gdb.reverse/readv-reverse.exp: Likewise.
	* gdb.reverse/recvmsg-reverse.exp: Likewise.
	* gdb.reverse/time-reverse.exp: Likewise.
	* gdb.reverse/waitpid-reverse.exp: Likewise and add KFAILs.