gnu: Change ld-wrapper extension from .scm to .in.

* gnu/packages/ld-wrapper.scm: Rename to...
* gnu/packages/ld-wrapper.in: ... this.
* gnu/packages/base.scm (make-ld-wrapper): Adjust "wrapper" input
  accordingly.
* gnu-system.am (GNU_SYSTEM_MODULES): Remove ld-wrapper.scm.
  (MISC_DISTRO_FILES): New variable.

gnu-system.am

@@ -162,7 +162,6 @@ GNU_SYSTEM_MODULES =				\
   gnu/packages/kde.scm				\
   gnu/packages/key-mon.scm			\
   gnu/packages/language.scm			\
-  gnu/packages/ld-wrapper.scm			\
   gnu/packages/less.scm				\
   gnu/packages/lesstif.scm			\
   gnu/packages/libcanberra.scm			\
@@ -566,6 +565,9 @@ dist_patch_DATA =						\
   gnu/packages/patches/xmodmap-asprintf.patch 			\
   gnu/packages/patches/zathura-plugindir-environment-variable.patch
 
+MISC_DISTRO_FILES =				\
+  gnu/packages/ld-wrapper.in
+
 bootstrapdir = $(guilemoduledir)/gnu/packages/bootstrap
 bootstrap_x86_64_linuxdir = $(bootstrapdir)/x86_64-linux
 bootstrap_i686_linuxdir = $(bootstrapdir)/i686-linux

gnu/packages/base.scm

@@ -375,7 +375,7 @@ TARGET is not #f, make a wrapper for the cross-linker for TARGET, called
               ("guile"    ,guile)
               ("bash"     ,bash)
               ("wrapper"  ,(search-path %load-path
-                                        "gnu/packages/ld-wrapper.scm"))))
+                                        "gnu/packages/ld-wrapper.in"))))
     (arguments
      `(#:guile ,guile-for-build
        #:modules ((guix build utils))