In llvm/llvm-project@7b23f413d1 , `.text`
started being suppressed from LLVM assembly in cases where it wasn't
strictly necessary. Currently, the sample functions in these two tests
are frequently decided to be IR-only functions, resulting in no code
generation, so LLVM drops the `.text` directive.
Adding `#[no_mangle]` forces these tests back to their original intent -
assembly code is generated, and so a `.text` directive is generated as
well.
On ELF, the text section is opened with ".text", on MachO with
".section __TEXT,__text".
Previously, on ELF this test was actually matching a GNU note
section, which is no longer emitted on Solaris starting with
LLVM 18.
Fixes https://github.com/rust-lang/rust/issues/120105.
