THRIFT-4759:add thrift export to fix windows shared lib building (#1714)

* add THRIFT_EXPORT to fix windows shared lib building
* use shared libraries on vs2017 appveyor build, leave msvc2017 static link
diff --git a/lib/cpp/Makefile.am b/lib/cpp/Makefile.am
index 616effd..114ff17 100755
--- a/lib/cpp/Makefile.am
+++ b/lib/cpp/Makefile.am
@@ -132,6 +132,7 @@
 include_thrift_HEADERS = \
                          $(top_builddir)/config.h \
                          src/thrift/thrift-config.h \
+                         src/thrift/thrift_export.h \
                          src/thrift/TDispatchProcessor.h \
                          src/thrift/Thrift.h \
                          src/thrift/TOutput.h \