compiler-rt: Add a comment explaining why we currently need weak linkage.

Author: alexrp

lib/compiler_rt/common.zig

@@ -3,6 +3,9 @@ const builtin = @import("builtin");
 const native_endian = builtin.cpu.arch.endian();
 const ofmt_c = builtin.object_format == .c;
 
+/// For now, we prefer weak linkage because some of the routines we implement here may also be
+/// provided by system/dynamic libc. Eventually we should be more disciplined about this on a
+/// per-symbol, per-target basis: https://github.com/ziglang/zig/issues/11883
 pub const linkage: std.builtin.GlobalLinkage = if (builtin.is_test)
     .internal
 else if (ofmt_c)