[m-rev.] diff: avoid more deprecated autoconf macros

[Julien Fischer]

Avoid more deprecated autoconf macros.

configure.ac:
      s/AC_FD_CC/AS_MESSAGE_LOG_FD/

INSTALL.git:
     Bump the minimum required version of autoconf.

Julien.

diff --git a/INSTALL.git b/INSTALL.git
index f2ee0b1..8cd1f93 100755
--- a/INSTALL.git
+++ b/INSTALL.git
@@ -7,7 +7,7 @@
  # Note: you need a previous version of Mercury already installed, since
  # the Git archive doesn't have all the necessary files for bootstrapping.
  #
-# You also need autoconf (version 2.58 or later) (and hence GNU m4) installed.
+# You also need autoconf (version 2.69 or later) (and hence GNU m4) installed.
  #
  # Step 1.  ./prepare.sh
  #
diff --git a/configure.ac b/configure.ac
index 6bd7188..e84a640 100644
--- a/configure.ac
+++ b/configure.ac
@@ -566,13 +566,13 @@ EOF
      unset MERCURY_STDLIB_DIR

      if
-        echo $BOOTSTRAP_MC conftest >&AC_FD_CC 2>&1 &&
+        echo $BOOTSTRAP_MC conftest >&AS_MESSAGE_LOG_FD 2>&1 &&
          $BOOTSTRAP_MC \
              --verbose \
              $link_static_opt conftest \
              --fixed-contiguity-2018-10-19 \
              --no-ssdb \
-            </dev/null >&AC_FD_CC 2>&1 &&
+            </dev/null >&AS_MESSAGE_LOG_FD 2>&1 &&
          test "`./conftest 2>&1 | tr -d '\015'`" = "Hello, world" &&
          $BOOTSTRAP_MC \
              --grade none.gc \
@@ -583,7 +583,7 @@ EOF
              --output-grade-string \
              --shlib-linker-install-name-flag "-dummy_flag" \
              --ranlib-flags "" \
-            </dev/null >&AC_FD_CC 2>&1
+            </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          AC_MSG_RESULT(yes)
      else
@@ -1001,7 +1001,7 @@ EOF

      AC_MSG_CHECKING(whether we can make error messages filterable)
      if $CC -ftrack-macro-expansion=0 -fno-diagnostics-show-caret -c conftest.c \
-        </dev/null >&AC_FD_CC 2>&1
+        </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          AC_MSG_RESULT(yes)
          CFLAGS_FOR_ERRMSG_FILTER="-ftrack-macro-expansion=0 -fno-diagnostics-show-caret"
@@ -1012,7 +1012,7 @@ EOF

      AC_MSG_CHECKING(whether we can use -fno-move-loop-invariants)
      if $CC -fno-move-loop-invariants -c conftest.c \
-        </dev/null >&AC_FD_CC 2>&1
+        </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          AC_MSG_RESULT(yes)
          CFLAGS_FOR_NO_MOVE_LOOP_INVARIANTS="-fno-move-loop-invariants"
@@ -1023,7 +1023,7 @@ EOF

      AC_MSG_CHECKING(whether we can use -fno-reorder-functions)
      if $CC -fno-reorder-functions -c conftest.c \
-        </dev/null >&AC_FD_CC 2>&1
+        </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          AC_MSG_RESULT(yes)
          CFLAGS_FOR_NO_REORDER_FUNCTIONS="-fno-reorder-functions"
@@ -1034,7 +1034,7 @@ EOF

      AC_MSG_CHECKING(whether we can use -fno-tree-dominator-opts)
      if $CC -fno-tree-dominator-opts -c conftest.c \
-        </dev/null >&AC_FD_CC 2>&1
+        </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          AC_MSG_RESULT(yes)
          CFLAGS_FOR_NO_TREE_DOMINATOR_OPTS="-fno-tree-dominator-opts"
@@ -2254,12 +2254,12 @@ AC_CACHE_VAL(mercury_cv_bzero_needs_strings_header, [
          }
  EOF

-    if $CC -c conftest.c < /dev/null >&AC_FD_CC 2>&1
+    if $CC -c conftest.c < /dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          mercury_cv_bzero_needs_strings_header=no
      else
          if $CC -DMR_BZERO_NEEDS_STRINGS_HEADER -c conftest.c \
-            < /dev/null >&AC_FD_CC 2>&1
+            < /dev/null >&AS_MESSAGE_LOG_FD 2>&1
          then
              mercury_cv_bzero_needs_strings_header=yes
          else
@@ -3994,8 +3994,8 @@ if test "$AS" != ""; then
      foo(x)
  EOF
      if
-        echo $AS conftest.s >&AC_FD_CC 2>&1 &&
-        $AS conftest.s </dev/null >&AC_FD_CC 2>&1
+        echo $AS conftest.s >&AS_MESSAGE_LOG_FD 2>&1 &&
+        $AS conftest.s </dev/null >&AS_MESSAGE_LOG_FD 2>&1
      then
          mercury_cv_asm_does_full_preprocessing="yes"
      else