Documentation PR for cfg_panic

src/conditional-compilation.md

@@ -208,6 +208,15 @@ production.  For example, it controls the behavior of the standard library's
 Set when the crate being compiled is being compiled with the `proc_macro`
 [crate type].
 
+### `panic`
+
+Key-value option set depending on the panic strategy. Note that more values may be added in the future.
+
+Example values:
+
+* `"abort"`
+* `"unwind"`
+
 ## Forms of conditional compilation
 
 ### The `cfg` attribute
@@ -253,6 +262,13 @@ fn on_32bit_unix() {
 fn needs_not_foo() {
   // ...
 }
+
+// This function is only included when the panic strategy is set to unwind
+#[cfg(panic = "unwind")]
+fn when_unwinding() {
+  // ...
+}
+
 ```
 
 The `cfg` attribute is allowed anywhere attributes are allowed.