Fix libinproctrace.so build on PPC

Fix libinproctrace.so build on PPC

The recent gnulib import caused a build failure of libinproctrace.so
on PPC:

    alloc.c:(.text+0x20): undefined reference to `rpl_malloc'
    alloc.c:(.text+0x70): undefined reference to `rpl_realloc'

This patch fixes the problem using the same workaround that was
previously used for free.