Deprecate non-thread-safe `tmpnam`

[tgross35]

Now that we get linker warnings, the following shows up:

warning: linker stderr: /usr/lib/gcc-cross/s390x-linux-gnu/14/../../../../s390x-linux-gnu/bin/ld: /checkout/target/s390x-unknown-linux-gnu/debug/deps/ctest-2b4e214b33ebd228.6vgf36pq173k6xsd10a2clvaj.0hetexw.rcgu.o: in function `ctest::generated_tests::ctest_foreign_fn_tmpnam':
         /checkout/target/s390x-unknown-linux-gnu/debug/build/libc-test-cd93a2bf0f73e50d/out/ctest_output.rs:216053:(.text._RNvNtCsdHcC3tdE9G5_5ctest15generated_tests23ctest_foreign_fn_tmpnam+0x18): the use of `tmpnam' is dangerous, better use `mkstemp'
  |
  = note: `#[warn(linker_messages)]` on by default
  = note: the `linker_messages` lint ignores `-D warnings`
warning: linker stdout: /usr/lib/gcc-cross/s390x-linux-gnu/14/../../../../s390x-linux-gnu/bin/ld: /checkout/target/s390x-unknown-linux-gnu/debug/deps/ctest-2b4e214b33ebd228.6vgf36pq173k6xsd10a2clvaj.0hetexw.rcgu.o: note: the message above does not take linker garbage collection into account

These are deprecated in glibc at least https://man7.org/linux/man-pages/man3/tmpnam.3.html. We should deprecate all instances of tmpnam, tempnam, and L_tmpnam since they have more secure alternatives, for removal in 1.0.

[tgross35]

Cc @dybucc as you have been doing a number of deprecations

[dybucc]

Do you mean to deprecate symbols that are deprecated upstream only? Or do you want to also deprecate symbols not recommended for use? Add mktemp in the latter case [1].

[tgross35]

Just the ones that are deprecated upstream, so we can remove them. There are quite a few bits of API that are no longer recommended but we probably should keep around, mktemp being one of them - maybe we'll deprecate them one day but that's something that can wait until any time after 1.0.

[mansiverma897993]

@tgross35 can you assign this issue to me ?? I would like to work on it