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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<tr><td><span title='2024-06-26 12:35:26 +0300'>2024-06-26</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=f0eb8fc162df3a6ecf0964a5e739e068f4c34b18'>gnu: musl: Install compiler wrappers.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2024-06-26 12:35:26 +0300'>2024-06-26</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=d2585eda996bf590fcc7b561f652cd783694d121'>gnu: musl: Install ldso symlink in correct location.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2024-06-23 13:33:24 +0800'>2024-06-23</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=36fcf6092f47ae5d4fad24b3f2f7025f6214a1c3'>gnu: musl: Enable gcc wrapper.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2024-06-12 00:03:36 +0200'>2024-06-12</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=f1b1c5fd6c4d92534080e0d8052aa4d6f2e6304d'>gnu: musl: Update to 1.2.5.</a><span class='msg-avail'>...</span></td><td>fanquake</td></tr>