This patch addresses another issue highlighted by the recent "isolate
erroneous path" patch applied to gcc trunk.
The failure mechanism is similar to:
https://sourceware.org/ml/libc-alpha/2013-11/msg00291.html
In this case htab_find_slot() may result in a call to calloc() and
hence may return NULL. The code in _dl_make_tlsdesc_dynamic does not
check the return value from htab_find_slot before dereferencing it.
The "isolate erroneous path" code in trunk gcc spots the ill defined
behaviour and inserts an abort(), this leads to a link error for at
least ARM and AArch64 builds of glibc.
This patch adds a check on the return value, I think the fix is
obvious, if I'll commit tomorrow if I don't get any objections.