gnu: rust: Use GDB 8.2 for tests.

* gnu/packages/gdb.scm (gdb-8.2): New public variable.
* gnu/packages/rust.scm (rust-1.27)[native-inputs]: Use GDB-8.2 instead of GDB.

gnu/packages/gdb.scm

@@ -106,6 +106,18 @@ (define-public gdb-8.3
 written in C, C++, Ada, Objective-C, Pascal and more.")
     (license gpl3+)))
 
+(define-public gdb-8.2
+  (package/inherit
+   gdb-8.3
+   (version "8.2.1")
+   (source (origin
+             (method url-fetch)
+             (uri (string-append "mirror://gnu/gdb/gdb-"
+                                 version ".tar.xz"))
+             (sha256
+              (base32
+               "00i27xqawjv282a07i73lp1l02n0a3ywzhykma75qg500wll6sha"))))))
+
 (define-public gdb
   ;; This is the fixed version that packages depend on.  Update it rarely
   ;; enough to avoid massive rebuilds.

gnu/packages/rust.scm

@@ -779,6 +779,9 @@ (define-public rust-1.27
                                        "rust-bootstrap-stage0-test.patch"
                                        "rust-1.25-accept-more-detailed-gdb-lines.patch"
                                        "rust-reproducible-builds.patch")))))
+      (native-inputs
+       (alist-replace "gdb" (list gdb-8.2)
+                      (package-native-inputs base-rust)))
       (arguments
        (substitute-keyword-arguments (package-arguments base-rust)
          ((#:phases phases)