Comment what's going on in dbghelp

Author: alexcrichton

build.rs

@@ -8,4 +8,6 @@ fn main() {
     //
     // <https://github.com/rust-lang/rust/pull/53910>
     ac.emit_rustc_version(1, 30);
-}
+
+    println!("cargo:rerun-if-changed=build.rs");
+}

src/symbolize/dbghelp.rs

@@ -10,13 +10,18 @@
 
 #![allow(bad_style)]
 
+// This is a hack for compatibility with rustc 1.25.0. The no_std mode of this
+// crate is not supported pre-1.30.0, but in std mode the `char` module here
+// moved in rustc 1.26.0 (ish). As a result, in std mode we use `std::char` to
+// retain compatibility with rustc 1.25.0, but in `no_std` mode (which is
+// 1.30.0+ already) we use `core::char`.
 #[cfg(feature = "std")]
 use std::char;
+#[cfg(not(feature = "std"))]
+use core::char;
 
 use core::mem;
 use core::slice;
-#[cfg(not(feature = "std"))]
-use core::char;
 
 use winapi::ctypes::*;
 use winapi::shared::basetsd::*;