Weakly export platform_version symbols

The symbols __isPlatformVersionAtLeast and __isOSVersionAtLeast.

This allows the user to link both compiler_rt and std.

library/std/src/sys/platform_version/darwin/public_extern.rs

@@ -77,6 +77,10 @@ use super::{current_version, pack_i32_os_version};
 // NOTE: This symbol has a workaround in the compiler's symbol mangling to avoid mangling it, while
 // still not exposing it from non-cdylib (like `#[no_mangle]` would).
 #[rustc_std_internal_symbol]
+// NOTE: Making this a weak symbol might not be entirely the right solution for this, `compiler_rt`
+// doesn't do that, it instead makes the symbol have "hidden" visibility. But since this is placed
+// in `libstd`, which might be used as a dylib, we cannot do the same here.
+#[linkage = "weak"]
 // extern "C" is correct, Clang assumes the function cannot unwind:
 // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.0/clang/lib/CodeGen/CGObjC.cpp#L3980
 //
@@ -145,6 +149,7 @@ pub(super) extern "C" fn __isPlatformVersionAtLeast(
 /// Old entry point for availability. Used when compiling with older Clang versions.
 // SAFETY: Same as for `__isPlatformVersionAtLeast`.
 #[rustc_std_internal_symbol]
+#[linkage = "weak"]
 pub(super) extern "C" fn __isOSVersionAtLeast(major: i32, minor: i32, subminor: i32) -> i32 {
     let version = pack_i32_os_version(major, minor, subminor);
     (version <= current_version()) as i32