Fix build for no-MMU targets

Fix build for no-MMU targets

Commit 7488ce9e23f1 "Check whether PTRACE_GET_SYSCALL_INFO is supported
by the kernel" added a fork() call in test_ptrace_get_syscall_info()
which is included in the main strace executable code.  Although the
test_ptrace_get_syscall_info() routine is not called on no-MMU targets,
the compiler can't optimize it out because it is a global symbol.
So build for no-MMU targets currently fails:

strace-ptrace_syscall_info.o: In function `test_ptrace_get_syscall_info':
ptrace_syscall_info.c:(.text+0x1c): undefined reference to `fork'

* ptrace_syscall_info.c (test_ptrace_get_syscall_info): Make
the definition depend on HAVE_FORK.
* strace.c (init): Call test_ptrace_get_syscall_info unconditionally.
* NEWS: Mention this fix.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>
Fixes: v4.26~50 "Check whether PTRACE_GET_SYSCALL_INFO is supported by the kernel"