main/imap: include linkage.c

needed by asterisk. ref #4840

main/imap/APKBUILD

@@ -5,7 +5,7 @@
 # build it shared
 pkgname=imap
 pkgver=2007f
-pkgrel=5
+pkgrel=6
 pkgdesc="An IMAP/POP server"
 url="http://www.washington.edu/imap"
 arch="all"
@@ -52,6 +52,7 @@ package() {
 		install -D -m644 c-client/$i.h \
 			"$pkgdir"/usr/include/imap/$i.h
 	done
+	install -m644 c-client/linkage.c "$pkgdir"/usr/include/imap/linkage.c
 
 	install -Dm755 c-client/libc-client.so.1.0.0 \
 		"$pkgdir"/usr/lib/libc-client.so.1.0.0 \