Without this patch, the 'make install' attempts to 'install' a directory, which causes an error.

diff --git a/c++/src/build-system/Makefile.in.top b/c++/src/build-system/Makefile.in.top
index 1abe44f..d6000b3 100644
--- a/c++/src/build-system/Makefile.in.top
+++ b/c++/src/build-system/Makefile.in.top
@@ -51,7 +51,7 @@ install-toolkit:
 	    done
 	cd $(includedir0) && find * -name CVS -prune -o -print |\
             cpio -pd $(pincludedir)
-	$(INSTALL) -m 644 $(incdir)/* $(pincludedir)
+	cp -R $(incdir)/* $(pincludedir)
 ## set up appropriate build and status directories somewhere under $(libdir)?
 
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<div class='path'>path: <a href='/guix/log/?id=091502f398df5739f5e07ac7f52efb09fdcf6b23'>root</a>/<a href='/guix/log/.guix-authorizations?id=091502f398df5739f5e07ac7f52efb09fdcf6b23'>.guix-authorizations</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/.guix-authorizations?id=091502f398df5739f5e07ac7f52efb09fdcf6b23&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-12-11 01:00:01 +0100'>2022-12-11</span></td><td><a href='/guix/commit/.guix-authorizations?id=6bb9424f22239a0a2f50133f8051c635bf9a409a'>.guix-authorizations: Authorise John Kehayias.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-11-08 08:52:22 -0500'>2022-11-08</span></td><td><a href='/guix/commit/.guix-authorizations?id=96ae718c516a289124a0b91ceeef78b20d187825'>authorizations: Remove old key for "davexunit".</a><span class='msg-avail'>...</span></td><td>David Thompson</td></tr>
<tr><td><span title='2022-08-11 21:48:10 +0200'>2022-08-11</span></td><td><a href='/guix/commit/.guix-authorizations?id=dd7a29faf3eece4d1a672946d421e2bb72f245cf'>.guix-authorizations: Authorize Andrew Tropin's subkey instead.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-08-05 18:32:45 +0300'>2022-08-05</span></td><td><a href='/guix/commit/.guix-authorizations?id=4fc41b4a9dbc422302bc44b7589722e43ec45cda'>.git-authorizations: Authorize Andrew Tropin.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>