SERVER-3331: On Windows, build the client driver, even if you cannot …

…find the boost libraries.

Boost headers provide information that MSVC can use to find the correct version of boost libraries,
so it does not matter if SCons cannot find the libraries.  Build anyways.

distsrc/client/SConstruct

@@ -44,16 +44,18 @@ env.Append(CPPDEFINES=[ "_SCONS", "MONGO_EXPOSE_MACROS" ])
 
 nix = False
 linux = False
-
+win = False
 
 if "darwin" == sys.platform:
     addExtraLibs( "/opt/local/" )
     nix = True
 elif sys.platform in ("linux2", "linux3"):
     nix = True
     linux = True
+elif sys.platform == 'win32':
+    win = True
 
-if sys.platform == 'win32':
+if win:
     env['DIST_ARCHIVE_SUFFIX'] = '.zip'
     env.Append(CCFLAGS=['/EHsc', '/O2'])
 else:
@@ -69,7 +71,8 @@ conf = Configure(env)
 for lib in boostLibs:
     if not conf.CheckLib(["boost_%s-mt" % lib, "boost_%s" % lib],
                          language="C++"):
-        Exit(1)
+        if not win:
+            Exit(1)
 conf.Finish()
 
 clientEnv = env.Clone()