[BOLT][AArch64] Fix ifuncs test header inclusion

[rafaelauler]

Summary: Do not include stdlib headers as these tests are built with -nostdlib. Tests outside of runtime folder also run cross-platforms, so an x86 machine wouldn't have access to the correct headers used in the aarch64 toolchain, even if it has an aarch64 compiler (clang itself).

[yota9]

Thanks @rafaelauler . Initially I've started to write runtime test and forgot to remove the lines. But saw it during preparing #71635 and fixed it, would be thankful for your approve so I won't have to rebase it. If there are some comments there fill free to submit your fix first.

[aaupov]

Thanks @rafaelauler . Initially I've started to write runtime test and forgot to remove the lines. But saw it during preparing #71635 and fixed it, would be thankful for your approve so I won't have to rebase it. If there are some comments there fill free to submit your fix first.

Let's unblock testing first. It should be trivial to merge, no need to bundle up this fix. Thanks for addressing it though.