Following up on r1888560, reverse default logic to avoid breaking the buildbots that have libserf-1.lib installed

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1888561 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/build/generator/gen_win_dependencies.py b/build/generator/gen_win_dependencies.py
index a6f6c9a..e5e2cf6 100644
--- a/build/generator/gen_win_dependencies.py
+++ b/build/generator/gen_win_dependencies.py
@@ -168,7 +168,7 @@
     self.disable_shared = None
     self.static_apr = None
     self.static_openssl = None
-    self.static_serf = None
+    self.shared_serf = None
     self.instrument_apr_pools = None
     self.instrument_purify_quantify = None
     self.sasl_path = None
@@ -226,11 +226,12 @@
         self.disable_shared = 1
       elif opt == '--with-static-apr':
         self.static_apr = 1
-        self.static_serf = 1 # Can't mix apr versions
+        self.shared_serf = 0 # Can't mix apr versions
       elif opt == '--with-static-openssl':
         self.static_openssl = 1
-      elif opt == '--with-static-serf':
-        self.static_serf = 1
+      elif opt == '--with-shared-serf':
+        if not self.static_apr:
+          self.shared_serf = 1
       elif opt == '-D':
         self.cpp_defines.append(val)
       elif opt == '--vsnet-version':
@@ -1339,7 +1340,7 @@
     else:
       lib_name = 'serf.lib'
     
-    if not self.static_serf and os.path.isfile(os.path.join(lib_dir, 'lib' + lib_name)):
+    if self.shared_serf:
       lib_name = 'lib' + lib_name
 
     defines = ['SVN_HAVE_SERF', 'SVN_LIBSVN_RA_LINKS_RA_SERF']
diff --git a/gen-make.py b/gen-make.py
index 5811705..72eacb7 100755
--- a/gen-make.py
+++ b/gen-make.py
@@ -206,6 +206,9 @@
   print("  --with-static-openssl")
   print("           Use static openssl")
   print("")
+  print("  --with-shared-serf")
+  print("           Use shared library version of serf")
+  print("")
   print("  --vsnet-version=VER")
   print("           generate for VS.NET version VER (2005-2017 or 9.0-15.0)")
   print("           [implies '-t vcproj']")
@@ -257,6 +260,7 @@
                             'with-apr_memcache=',
                             'with-static-apr',
                             'with-static-openssl',
+                            'with-shared-serf',
                             'enable-pool-debug',
                             'enable-purify',
                             'enable-quantify',