Get rid of all mention of `mk/config.h`

The RTS configure script is now solely responsible for managing its
headers; the top level configure script does not help.

.gitignore

@@ -184,8 +184,8 @@ _darcs/
 /linter.log
 /mk/are-validating.mk
 /mk/build.mk
-/mk/config.h
-/mk/config.h.in
+/mk/unused.h
+/mk/unused.h.in
 /mk/config.mk
 /mk/config.mk.old
 /mk/system-cxx-std-lib-1.0.conf

configure.ac

@@ -32,8 +32,8 @@ AC_CONFIG_MACRO_DIRS([m4])
 # checkout), then we ship a file 'VERSION' containing the full version
 # when the source distribution was created.
 
-if test ! -f mk/config.h.in; then
-   echo "mk/config.h.in doesn't exist: perhaps you haven't run 'python3 boot'?"
+if test ! -f rts/ghcautoconf.h.autoconf.in; then
+   echo "rts/ghcautoconf.h.autoconf.in doesn't exist: perhaps you haven't run 'python3 boot'?"
    exit 1
 fi
 
@@ -99,8 +99,8 @@ AC_PREREQ([2.69])
 # Prepare to generate the following header files
 #
 
-# This one is autogenerated by autoheader.
-AC_CONFIG_HEADER(mk/config.h)
+dnl so the next one doesn't get mangled
+AC_CONFIG_HEADER(mk/unused.h)
 # This one is manually maintained.
 AC_CONFIG_HEADER(compiler/ghc-llvm-version.h)
 dnl manually outputted above, for reasons described there.

distrib/cross-port

@@ -28,7 +28,7 @@ if [ ! -f b1-stamp ]; then
 
    # For cross-compilation, at this stage you may want to set up a source
    # tree on the target machine, run the configure script there, and bring
-   # the resulting mk/config.h file back into this tree before building
+   # the resulting rts/ghcautoconf.h.autoconf file back into this tree before building
    # the libraries.
 
    touch mk/build.mk

rts/configure.ac

@@ -393,9 +393,9 @@ touch include/ghcautoconf.h
 
 echo "#if !defined(__GHCAUTOCONF_H__)" >> include/ghcautoconf.h
 echo "#define __GHCAUTOCONF_H__" >> include/ghcautoconf.h
-# Copy the contents of $srcdir/../mk/config.h, turning '#define PACKAGE_FOO
+# Copy the contents of ghcautoconf.h.autoconf, turning '#define PACKAGE_FOO
 # "blah"' into '/* #undef PACKAGE_FOO */' to avoid clashes.
-cat $srcdir/../mk/config.h ghcautoconf.h.autoconf | sed \
+cat ghcautoconf.h.autoconf | sed \
    -e 's,^\([	 ]*\)#[	 ]*define[	 ][	 ]*\(PACKAGE_[A-Z]*\)[	 ][ 	]*".*".*$,\1/* #undef \2 */,' \
    -e '/__GLASGOW_HASKELL/d' \
    -e '/REMOVE ME/d' \