[PATCH v2] elf: Use the minimal malloc on tunables_strdup

[Joseph Myers]

This seems to have caused build failures for many architectures (plus a 
localplt test failure for i686-gnu, "Missing required PLT reference: 
ld.so: __sbrk").

https://sourceware.org/pipermail/libc-testresults/2021q4/008843.html

alpha-linux-gnu seems representative of the build failures:

dl-minimal.c: In function '__chk_fail':
dl-minimal.c:168:3: error: implicit declaration of function '_exit' [-Werror=implicit-function-declaration]
  168 |   _exit (127);
      |   ^~~~~
dl-minimal.c:168:3: error: incompatible implicit declaration of built-in function '_exit' [-Werror=builtin-declaration-mismatch]
In file included from <command-line>:
dl-minimal.c: At top level:
./../include/libc-symbols.h:549:33: error: '__EI___libc_fatal' aliased to undefined symbol '__GI___libc_fatal'
  549 |   extern thread __typeof (name) __EI_##name \
      |                                 ^~~~~
./../include/libc-symbols.h:545:3: note: in expansion of macro '__hidden_ver2'
  545 |   __hidden_ver2 (, local, internal, name)
      |   ^~~~~~~~~~~~~
./../include/libc-symbols.h:554:41: note: in expansion of macro '__hidden_ver1'
  554 | #  define hidden_def(name)              __hidden_ver1(__GI_##name, name, name);
      |                                         ^~~~~~~~~~~~~
./../include/libc-symbols.h:646:32: note: in expansion of macro 'hidden_def'
  646 | # define rtld_hidden_def(name) hidden_def (name)
      |                                ^~~~~~~~~~
dl-minimal.c:162:1: note: in expansion of macro 'rtld_hidden_def'
  162 | rtld_hidden_def (__libc_fatal)
      | ^~~~~~~~~~~~~~~

-- 
Joseph S. Myers
joseph@codesourcery.com