Compile error with gcc 4.4.7

[tueda]

msgpack-c fails to build with gcc 4.4.7 when compiled without C++11:

[ 54%] Building CXX object example/cpp03/CMakeFiles/simple.dir/simple.cpp.o
cc1plus: error: unrecognized command line option "-std=c++03"

Actually I can't find -std=c++03 in the document of gcc 4.4.7: https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/C-Dialect-Options.html#C-Dialect-Options, although a backport for that flag may be provided in some systems.

[redboltz]

@tueda , thank you for reporting the issue.
I think that -std=c++03 should be replaced with -std=c++98.
I will fix it.

[redboltz]

@tueda , could you check #545 ?

[tueda]

@redboltz the fix works to me. Thank you.