Add additional information about Rust implementation

Author: arlosi

Diff for: src/debugging-support-in-rustc.md

@@ -280,20 +280,29 @@ The hash can also be used to prove that a given source file has not been modifie
 used to compile an executable. Because MD5 and SHA1 both have demonstrated vulnerabilities,
 using SHA256 is recommended for this application.
 
+The Rust compiler stores the hash for each source file in the corresponding `SourceFile` in
+the `SourceMap`. The hashes of input files to external crates are stored in `rlib` metadata.
+
+A default hashing algorithm is set in the target specification. This allows the target to
+specify the best hash available, since not all targets support all hash algorithms.
+
+The hashing algorithm for a target can also be overridden with the `-Z source-file-checksum=`
+command-line option.
+
 #### DWARF 5
 DWARF version 5 supports embedding an MD5 hash to validate the source file version in use.
 DWARF 5 - Section 6.2.4.1 opcode DW_LNCT_MD5
 
 #### LLVM
-LLVM IR supports MD5, SHA1, and SHA256 source file checksums in the DIFile node.
+LLVM IR supports MD5 and SHA1 (and SHA256 in LLVM 11+) source file checksums in the DIFile node.
 
-LLVM DIFile documentation: [https://llvm.org/docs/LangRef.html#difile]
+[LLVM DIFile documentation](https://llvm.org/docs/LangRef.html#difile)
 
 #### Microsoft Visual C++ Compiler /ZH option
 The MSVC compiler supports embedding MD5, SHA1, or SHA256 hashes in the PDB using the `/ZH`
 compiler option.
 
-MSVC /ZH documentation: [https://docs.microsoft.com/en-us/cpp/build/reference/zh]
+[MSVC /ZH documentation](https://docs.microsoft.com/en-us/cpp/build/reference/zh)
 
 #### Clang
 Clang always embeds an MD5 checksum, though this does not appear in documentation.
@@ -345,5 +354,3 @@ to do this bridge but may have to add some mode to let the compiler understand s
 [Apple developer documentation for System Integrity Protection]: https://developer.apple.com/library/archive/releasenotes/MacOSX/WhatsNewInOSX/Articles/MacOSX10_11.html#//apple_ref/doc/uid/TP40016227-SW11
 [https://github.com/rust-lang/lldb]: https://github.com/rust-lang/lldb
 [https://github.com/rust-lang/llvm-project]: https://github.com/rust-lang/llvm-project
-[https://llvm.org/docs/LangRef.html#difile]: https://llvm.org/docs/LangRef.html#difile
-[https://docs.microsoft.com/en-us/cpp/build/reference/zh]: https://docs.microsoft.com/en-us/cpp/build/reference/zh