gdbserver/linux: free process_info_private and arch_process_info when failing to...

gdbserver/linux: free process_info_private and arch_process_info when failing to attach

Running

  $ ../gdbserver/gdbserver --once --attach :1234 539436

with ASan while /proc/sys/kernel/yama/ptrace_scope is set to 1 (prevents
attaching) shows that we fail to free some platform-specific objects
tied to the process_info (process_info_private and arch_process_info):

    Direct leak of 32 byte(s) in 1 object(s) allocated from:
        #0 0x7f6b558b3fb9 in __interceptor_calloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
        #1 0x562eaf15d04a in xcalloc /home/simark/src/binutils-gdb/gdbserver/../gdb/alloc.c:100
        #2 0x562eaf251548 in xcnew<process_info_private> /home/simark/src/binutils-gdb/gdbserver/../gdbsupport/poison.h:122
        #3 0x562eaf22810c in linux_process_target::add_linux_process_no_mem_file(int, int) /home/simark/src/binutils-gdb/gdbserver/linux-low.cc:426
        #4 0x562eaf22d33f in linux_process_target::attach(unsigned long) /home/simark/src/binutils-gdb/gdbserver/linux-low.cc:1132
        #5 0x562eaf1a7222 in attach_inferior /home/simark/src/binutils-gdb/gdbserver/server.cc:308
        #6 0x562eaf1c1016 in captured_main /home/simark/src/binutils-gdb/gdbserver/server.cc:3949
        #7 0x562eaf1c1d60 in main /home/simark/src/binutils-gdb/gdbserver/server.cc:4084
        #8 0x7f6b552f630f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)

    Indirect leak of 56 byte(s) in 1 object(s) allocated from:
        #0 0x7f6b558b3fb9 in __interceptor_calloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
        #1 0x562eaf15d04a in xcalloc /home/simark/src/binutils-gdb/gdbserver/../gdb/alloc.c:100
        #2 0x562eaf2a0d79 in xcnew<arch_process_info> /home/simark/src/binutils-gdb/gdbserver/../gdbsupport/poison.h:122
        #3 0x562eaf295e2c in x86_target::low_new_process() /home/simark/src/binutils-gdb/gdbserver/linux-x86-low.cc:723
        #4 0x562eaf22819b in linux_process_target::add_linux_process_no_mem_file(int, int) /home/simark/src/binutils-gdb/gdbserver/linux-low.cc:428
        #5 0x562eaf22d33f in linux_process_target::attach(unsigned long) /home/simark/src/binutils-gdb/gdbserver/linux-low.cc:1132
        #6 0x562eaf1a7222 in attach_inferior /home/simark/src/binutils-gdb/gdbserver/server.cc:308
        #7 0x562eaf1c1016 in captured_main /home/simark/src/binutils-gdb/gdbserver/server.cc:3949
        #8 0x562eaf1c1d60 in main /home/simark/src/binutils-gdb/gdbserver/server.cc:4084
        #9 0x7f6b552f630f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)

Those objects are deleted by linux_process_target::mourn, but that is
not called if we fail to attach, we only call remove_process.  I
initially fixed this by making linux_process_target::attach call
linux_process_target::mourn on failure (before calling error).  But this
isn't done anywhere else (including in GDB) so it would just be
confusing to do things differently here.

Instead, add a linux_process_target::remove_linux_process helper method
(which calls remove_process), and call that instead of remove_process in
the Linux target.  Move the free-ing of the extra data from the mourn
method to that new method.

Change-Id: I277059a69d5f08087a7f3ef0b8f1792a1fcf7a85