Followup to r1902335/issue #4901, more missing dependencies: install-serf-lib

* build.conf:
  (libsvn_ra_serf): add install dependency on $(SVN_FS_LIB_INSTALL_DEPS)


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1902364 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/build.conf b/build.conf
index df3a9cf..150b63f 100644
--- a/build.conf
+++ b/build.conf
@@ -340,6 +340,7 @@
 path = subversion/libsvn_ra_serf
 install = serf-lib
 libs = libsvn_delta libsvn_subr aprutil apriconv apr serf zlib
+add-install-deps = $(SVN_FS_LIB_INSTALL_DEPS)
 msvc-static = yes
 
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