A simpler way to make the "arch" build directory

This implements a simpler way to make the "arch" build directory --
namely, now it is done as an order-only dependency in the Makefile,
rather than being created when config.status is run.  This simpler
because it means that the build directories can be changed without
re-running autoconf.

ChangeLog
2017-11-27  Tom Tromey  <tom@tromey.com>

	* configure.ac (CONFIG_SRC_SUBDIR): Don't subst.
	* configure: Rebuild.
	* Makefile.in (CONFIG_SRC_SUBDIR): Redefine.
	(CONFIG_DEP_SUBDIR): New variable.
	(%.o): Add order-only dependency.
	($(CONFIG_DEP_SUBDIR)): New target.

4 files changed, 17 insertions, 28 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6134efc..e3c5063 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2017-11-27  Tom Tromey  <tom@tromey.com>
+
+	* configure.ac (CONFIG_SRC_SUBDIR): Don't subst.
+	* configure: Rebuild.
+	* Makefile.in (CONFIG_SRC_SUBDIR): Redefine.
+	(CONFIG_DEP_SUBDIR): New variable.
+	(%.o): Add order-only dependency.
+	($(CONFIG_DEP_SUBDIR)): New target.
+
 2017-11-26  Dominik Czarnota  <dominik.b.czarnota@gmail.com>
 
 	PR gdb/21945
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 7198556..bbe4287 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -645,9 +645,11 @@ CONFIG_ALL = @CONFIG_ALL@
 CONFIG_CLEAN = @CONFIG_CLEAN@
 CONFIG_INSTALL = @CONFIG_INSTALL@
 CONFIG_UNINSTALL = @CONFIG_UNINSTALL@
-CONFIG_SRC_SUBDIR = @CONFIG_SRC_SUBDIR@
 HAVE_NATIVE_GCORE_TARGET = @HAVE_NATIVE_GCORE_TARGET@
 
+CONFIG_SRC_SUBDIR = arch
+CONFIG_DEP_SUBDIR = $(addsuffix /$(DEPDIR),$(CONFIG_SRC_SUBDIR))
+
 # -I. for config files.
 # -I$(srcdir) for gdb internal headers.
 # -I$(srcdir)/config for more generic config files.
@@ -1927,10 +1929,14 @@ all: gdb$(EXEEXT) $(CONFIG_ALL)
 	@$(MAKE) $(FLAGS_TO_PASS) DO=all "DODIRS=`echo $(SUBDIRS) | sed 's/testsuite//'`" subdir_do
 
 # Rule for compiling .c files in the top-level gdb directory.
-%.o: %.c
+# The order-only dependencies ensure that we create the build subdirectories.
+%.o: %.c | $(CONFIG_DEP_SUBDIR)
 	$(COMPILE) $<
 	$(POSTCOMPILE)
 
+$(CONFIG_DEP_SUBDIR):
+	$(SHELL) $(srcdir)/../mkinstalldirs $@
+
 # Rules for compiling .c files in the various source subdirectories.
 %.o: $(srcdir)/cli/%.c
 	$(COMPILE) $<
diff --git a/gdb/configure b/gdb/configure
index 55544fb..7655b45 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -736,7 +736,6 @@ LIBINTL_DEP
 LIBINTL
 USE_NLS
 CCDEPMODE
-CONFIG_SRC_SUBDIR
 DEPDIR
 am__leading_dot
 CXX_DIALECT
@@ -5958,13 +5957,6 @@ DEPDIR="${am__leading_dot}deps"
 ac_config_commands="$ac_config_commands depdir"
 
 
-# Create sub-directories for objects and dependencies.
-CONFIG_SRC_SUBDIR="arch"
-
-
-ac_config_commands="$ac_config_commands gdbdepdir"
-
-
 depcc="$CC"   am_compiler_list=
 
 am_depcomp=$ac_aux_dir/depcomp
@@ -18512,7 +18504,6 @@ cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 # INIT-COMMANDS
 #
 ac_aux_dir=$ac_aux_dir DEPDIR=$DEPDIR
-ac_aux_dir=$ac_aux_dir DEPDIR=$DEPDIR CONFIG_SRC_SUBDIR="$CONFIG_SRC_SUBDIR"
 
 _ACEOF
 
@@ -18524,7 +18515,6 @@ do
   case $ac_config_target in
     "config.h") CONFIG_HEADERS="$CONFIG_HEADERS config.h:config.in" ;;
     "depdir") CONFIG_COMMANDS="$CONFIG_COMMANDS depdir" ;;
-    "gdbdepdir") CONFIG_COMMANDS="$CONFIG_COMMANDS gdbdepdir" ;;
     "jit-reader.h") CONFIG_FILES="$CONFIG_FILES jit-reader.h:jit-reader.in" ;;
     "$ac_config_links_1") CONFIG_LINKS="$CONFIG_LINKS $ac_config_links_1" ;;
     "gcore") CONFIG_FILES="$CONFIG_FILES gcore" ;;
@@ -19148,11 +19138,6 @@ $as_echo "$as_me: executing $ac_file commands" >&6;}
 
   case $ac_file$ac_mode in
     "depdir":C) $SHELL $ac_aux_dir/mkinstalldirs $DEPDIR ;;
-    "gdbdepdir":C)
-  for subdir in ${CONFIG_SRC_SUBDIR}
-  do
-      $SHELL $ac_aux_dir/mkinstalldirs $subdir/$DEPDIR
-  done ;;
     "gcore":F) chmod +x gcore ;;
     "Makefile":F)
 case x$CONFIG_HEADERS in
diff --git a/gdb/configure.ac b/gdb/configure.ac
index d43899c..5ded21a 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -44,17 +44,6 @@ AX_CXX_COMPILE_STDCXX(11, , mandatory)
 
 # Dependency checking.
 ZW_CREATE_DEPDIR
-# Create sub-directories for objects and dependencies.
-CONFIG_SRC_SUBDIR="arch"
-AC_SUBST(CONFIG_SRC_SUBDIR)
-
-AC_CONFIG_COMMANDS([gdbdepdir],[
-  for subdir in ${CONFIG_SRC_SUBDIR}
-  do
-      $SHELL $ac_aux_dir/mkinstalldirs $subdir/$DEPDIR
-  done],
-  [ac_aux_dir=$ac_aux_dir DEPDIR=$DEPDIR CONFIG_SRC_SUBDIR="$CONFIG_SRC_SUBDIR"])
-
 ZW_PROG_COMPILER_DEPENDENCIES([CC])
 
 gnulib_extra_configure_args=