Add hash of source files in debug info

* Adds either an MD5 or SHA1 hash to the debug info.
* Adds new unstable option `-Z src-hash-algorithm` to control the hashing algorithm.

src/test/codegen/remap_path_prefix/main.rs

@@ -22,7 +22,7 @@ fn main() {
 }
 
 // Here we check that local debuginfo is mapped correctly.
-// CHECK: !DIFile(filename: "/the/src/remap_path_prefix/main.rs", directory: "/the/cwd/")
+// CHECK: !DIFile(filename: "/the/src/remap_path_prefix/main.rs", directory: "/the/cwd/"
 
 // And here that debuginfo from other crates are expanded to absolute paths.
-// CHECK: !DIFile(filename: "/the/aux-src/remap_path_prefix_aux.rs", directory: "")
+// CHECK: !DIFile(filename: "/the/aux-src/remap_path_prefix_aux.rs", directory: ""

src/test/codegen/remap_path_prefix/xcrate-generic.rs

@@ -11,4 +11,4 @@ pub fn foo() {
 }
 
 // Here we check that local debuginfo is mapped correctly.
-// CHECK: !DIFile(filename: "/the/aux-src/xcrate-generic.rs", directory: "")
+// CHECK: !DIFile(filename: "/the/aux-src/xcrate-generic.rs", directory: ""

src/test/codegen/src-hash-algorithm/src-hash-algorithm-md5.rs

@@ -0,0 +1,6 @@
+// compile-flags: -g -Z src-hash-algorithm=md5
+
+#![crate_type = "lib"]
+
+pub fn test() {}
+// CHECK: checksumkind: CSK_MD5

src/test/codegen/src-hash-algorithm/src-hash-algorithm-sha1.rs

@@ -0,0 +1,6 @@
+// compile-flags: -g -Z src-hash-algorithm=sha1
+
+#![crate_type = "lib"]
+
+pub fn test() {}
+// CHECK: checksumkind: CSK_SHA1