[binutils-gdb] Remove cleanups from break-catch-syscall.c

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 3d415c26bad3a15eed00d2ddf85c4268df77a4cc ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 3d415c26bad3a15eed00d2ddf85c4268df77a4cc

Remove cleanups from break-catch-syscall.c

This removes the remaining cleanups from break-catch-syscall.c by
storing temporary strings in a vector.

ChangeLog
2017-10-19  Tom Tromey  <tom@tromey.com>

	* break-catch-syscall.c (catch_syscall_completer): Use
	std::string, gdb::unique_xmalloc_ptr.