top-level configure: setup target_configdirs based on repository

The top-level configure script is shared between the gcc repository
and the binutils-gdb repository.

The target_configdirs variable in the configure.ac script, defines
sub-directories that contain components that should be built for the
target using the target tools.

Some components, e.g. zlib, are built as both host and target
libraries.

This causes problems for binutils-gdb.  If we run 'make all' in the
binutils-gdb repository we end up trying to build a target version of
the zlib library, which requires the target compiler be available.
Often the target compiler isn't immediately available, and so the
build fails.

The problem with zlib impacted a previous attempt to synchronise the
top-level configure scripts from gcc to binutils-gdb, see this thread:

  https://sourceware.org/pipermail/binutils/2019-May/107094.html

And I'm in the process of importing libbacktrace in to binutils-gdb,
which is also a host and target library, and triggers the same issues.

I believe that for binutils-gdb, at least at the moment, there are no
target libraries that we need to build.

In the configure script we build three lists of things we want to
build, $configdirs, $build_configdirs, and $target_configdirs, we also
build two lists of things we don't want to build, $skipdirs and
$noconfigdirs.  We then remove anything that is in the lists of things
not to build, from the list of things that should be built.

My proposal is to add everything in target_configdirs into skipdirs,
if the source tree doesn't contain a gcc/ sub-directory.  The result
is that for binutils-gdb no target tools or libraries will be built,
while for the gcc repository, nothing should change.

If a user builds a unified source tree, then the target tools and
libraries should still be built as the gcc/ directory will be present.

I've tested a build of gcc on x86-64, and the same set of target
libraries still seem to get built.  On binutils-gdb this change
resolves the issues with 'make all'.

ChangeLog:

	* configure: Regenerate.
	* configure.ac (skipdirs): Add the contents of target_configdirs if
	we are not building gcc.

2 files changed, 20 insertions, 0 deletions

diff --git a/configure b/configure
index fcec657..787fcf8 100755
--- a/configure
+++ b/configure
@@ -6848,6 +6848,16 @@ case ,${enable_languages}, in
     ;;
 esac
 
+# If gcc/ is not in the source tree then we'll not be building a
+# target compiler, assume in that case we don't want to build any
+# target libraries or tools.
+#
+# This was added primarily for the benefit for binutils-gdb who reuse
+# this configure script, but don't always have target tools available.
+if test ! -d ${srcdir}/gcc; then
+   skipdirs="${skipdirs} ${target_configdirs}"
+fi
+
 # Remove the entries in $skipdirs and $noconfigdirs from $configdirs,
 # $build_configdirs and $target_configdirs.
 # If we have the source for $noconfigdirs entries, add them to $notsupp.
diff --git a/configure.ac b/configure.ac
index 1b1aa80..2b10e9a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2233,6 +2233,16 @@ case ,${enable_languages}, in
     ;;
 esac
 
+# If gcc/ is not in the source tree then we'll not be building a
+# target compiler, assume in that case we don't want to build any
+# target libraries or tools.
+#
+# This was added primarily for the benefit for binutils-gdb who reuse
+# this configure script, but don't always have target tools available.
+if test ! -d ${srcdir}/gcc; then
+   skipdirs="${skipdirs} ${target_configdirs}"
+fi
+
 # Remove the entries in $skipdirs and $noconfigdirs from $configdirs,
 # $build_configdirs and $target_configdirs.
 # If we have the source for $noconfigdirs entries, add them to $notsupp.