malloc: Fix malloc debug for 2.35 onwards

malloc: Fix malloc debug for 2.35 onwards

The change 1e5a5866cb ("Remove malloc hooks [BZ #23328]") has broken
ports that are using GLIBC_2_35, like the new OpenRISC port I am working
on.

The libc_malloc_debug.so library used to bring in the debug
infrastructure is currently essentially empty for GLIBC_2_35 ports like
mine causing mtrace tests to fail:

    cat sysdeps/unix/sysv/linux/or1k/shlib-versions
    DEFAULT                 GLIBC_2.35
    ld=ld-linux-or1k.so.1

    FAIL: posix/bug-glob2-mem
    FAIL: posix/bug-regex14-mem
    FAIL: posix/bug-regex2-mem
    FAIL: posix/bug-regex21-mem
    FAIL: posix/bug-regex31-mem
    FAIL: posix/bug-regex36-mem
    FAIL: malloc/tst-mtrace.

The issue seems to be with the ifdefs in malloc/malloc-debug.c. The
ifdefs are currently essentially exluding all symbols for ports > 2.35.

Removing the top level SHLIB_COMPAT ifdef allows things to just work.

Fixes: 1e5a5866cb ("Remove malloc hooks [BZ #23328]")
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>