Fix for #798

[cinemast]

Add preprocessor definitions for MSVC dllexport/dllimport statements

[cinemast]

I don't know why the gcc build is failing. It does not seem to be related to the changes.

[cdunn2001]

TravisCI might have deleted gcc-4.9. I'm asking them for advice on how to proceed.

[cdunn2001]

This passed 6 days ago: https://travis-ci.org/open-source-parsers/jsoncpp/builds/393044263?utm_source=github_status&utm_medium=notification

Maybe TravisCI changed very recently.

[cdunn2001]

Hmmm. This is strange. Your base commit rebuilds fine:

• https://travis-ci.org/cdunn2001/jsoncpp/builds/387473945

I've rebased your change onto our master, and it still fails:

• https://travis-ci.org/open-source-parsers/jsoncpp/jobs/395927931

I think the problem may be the '' here (after fPIC):

g++-4.9 -Ijsoncpp@sha -I. -I.. -I../include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall\
 -Winvalid-pch -Wnon-virtual-dtor -std=c++11 -O0 -g -fPIC ''  -MD \
 -MQ 'jsoncpp@sha/src_lib_json_json_value.cpp.o' \
 -MF 'jsoncpp@sha/src_lib_json_json_value.cpp.o.d' \
 -o 'jsoncpp@sha/src_lib_json_json_value.cpp.o' -c ../src/lib_json/json_value.cpp

I think your new string is being substituted wrong...

[cdunn2001]

Yes, a successful run has this:

[1/9] g++-4.9 -Ijsoncpp_test@exe -I. -I.. -I../include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -std=c++11 -O3  -MD -MQ 'jsoncpp_test@exe/src_test_lib_json_jsontest.cpp.o' -MF 'jsoncpp_test@exe/src_test_lib_json_jsontest.cpp.o.d' -o 'jsoncpp_test@exe/src_test_lib_json_jsontest.cpp.o' -c ../src/test_lib_json/jsontest.cpp

For some reason, clang doesn't mind the empty-string argument, but g++ has a problem with it.

[cdunn2001]

Meson needs [] instead of '' for empty-string. Fixing in #800.