Rework link.unwinding

This reworks this section to change the emphasis on "using non-rustc
linkers". To me, that seemed confusing, since this also applies to using
rustc (just that rustc automatically validates and generates an error if
it is validated).

Author: ehuss

src/linkage.md

@@ -279,10 +279,7 @@ r[link.unwinding]
 ### Prohibited linkage and unwinding
 
 r[link.unwinding.intro]
-If you are *not* using `rustc` to link Rust files, you must take care to ensure that unwinding is
-handled consistently across the entire binary. Linking without `rustc` includes using `dlopen` or similar facilities
-where linking is done by the system runtime without `rustc` being involved. In the following,
-we define what exactly is meant by "handling unwinding consistently".
+Panic unwinding must be supported consistently across the binary per the following rules.
 
 r[link.unwinding.potential]
 A Rust artifact is called *potentially unwinding* if any of the following conditions is met:
@@ -301,8 +298,9 @@ r[link.unwinding.prohibited]
 If a Rust artifact is potentially unwinding, then all its crates must be built with the `unwind` [panic strategy].
 
 > [!NOTE]
-> This restriction can only be violated when mixing code with different [`-C panic`] flags
-> while also using a non-`rustc` linker. Most users do not have to be concerned about this.
+> If you are *not* using `rustc` to link, you must take care to ensure that unwinding is handled consistently across the entire binary. Linking without `rustc` includes using `dlopen` or similar facilities where linking is done by the system runtime without `rustc` being involved.
+>
+> This can only happen when mixing code with different [`-C panic`] flags, so most users do not have to be concerned about this.
 
 > [!NOTE]
 > To guarantee that a library will be sound (and linkable with `rustc`)

src/panic.md

@@ -49,8 +49,8 @@ The _panic strategy_ defines the kind of panic runtime that a crate is built to
 > [!NOTE]
 > When compiling code with the `abort` panic strategy, the optimizer may assume that unwinding across Rust frames is impossible, which can result in both code-size and runtime speed improvements.
 
-r[panic.strategy.mixed]
-When linking with the `unwind` runtime, all crates must be built with the `unwind` strategy.
+> [!NOTE]
+> See [link.unwinding] for restrictions on linking crates with different panic strategies. An implication is that crates built with the `unwind` strategy can use the `abort` runtime, but not vice-versa.
 
 r[panic.unwind]
 ## Unwinding