Fixes for release

* Restore 0-fill of DX arrays

* Restore non-merging of pathnames in self-build.
  (Make the code match the comment)

* Unbreak #+msan

NEWS

@@ -4,10 +4,6 @@ changes relative to sbcl-2.1.4:
   * optimization: file compilation now produces smaller fasls for files which
     reference package literals.
   * optimization: faster function calls on ARM64.
-  * incompatible change: on certain platforms (currently just x86-64),
-    dynamic-extent arrays specialized on character and numeric types and
-    created without either :INITIAL-ELEMENT or :INITIAL-CONTENTS will reflect
-    previous contents of the stack instead of #\null (or 0) in all elements.
   * bug fix: on x86-64, fix instruction encoding for TEST on RIP-relative
     addresses.  (lp#1925808, reported by Shinmera on #sbcl, thanks also to 3b)
 

src/compiler/array-tran.lisp

@@ -916,7 +916,8 @@
                                (t
                                 ;; otherwise, reading an element can't cause an invalid bit pattern
                                 ;; to be observed, but the bits could be random.
-                                data-alloc-form))))))
+                                ;; KLUDGE: backward-compatibile 0-fill
+                                `(sb-vm::splat ,data-alloc-form nwords 0)))))))
 
             ;; Case (3) - constant :INITIAL-CONTENTS and LENGTH
             ((and c-length

src/compiler/main.lisp

@@ -843,7 +843,7 @@ necessary, since type inference may take arbitrarily long to converge.")
 ;;; The normal build sets it to T in make-target-2, despite that I think most people would
 ;;; prefer the nonstandard behavior. The standard behavior makes stored pathnames all wrong
 ;;; when files are physically moved. (Same problem as SBCL_HOME embedded into C pretty much)
-(defglobal *merge-pathnames* t)
+(defglobal *merge-pathnames* nil)
 
 ;;; Given a pathname, return a SOURCE-INFO structure.
 (defun make-file-source-info (file external-format &optional form-tracking-p)

src/compiler/x86-64/alloc.lisp

@@ -550,7 +550,7 @@
         (inst xor rdi rsp-tn) ; compute shadow address
         (zeroize rax)
         (inst rep)
-        (inst stos rax)))))
+        (inst stos :qword)))))
 
 ;;; ALLOCATE-LIST
 (macrolet ((calc-size-in-bytes (length answer)