Solve some problems about cmake build type (debug/release)

[dota17]

1. Solve the problem of testcase failure during cmake release-building.
When I run:

cmake -DCMAKE_BUILD_TYPR=Release ..
make
make test

two testcases (test_deep_copy.c / test_json_pointer.c) failed. This is due to NDEBUG macro. When we set -DCMAKE_BUILD_TYPR=Release, this macro will be defined globally by dafault. NDEBUG will make assert() macro invalid. And, at the same time, these two testcases use assert() irregularly. We should avoid function-calling, variable assignment or some operator(++...) in assert( ).

In fact, json-c already consider this issue. emmmm, I think -UNDEBUG is not a valid parameter/option. It does not work.

json-c/tests/CMakeLists.txt

Line 57 in 30e00cf

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -UNDEBUG")

The solution is shown in #547 . Maybe we should also modify all testcase, include: the including of <assert.h> and correct useage of assert().

2. Set default CMAKE_BUILD_TYPE and add the default compilation optimization options.
The default CMAKE_BUILD_TYPE can be set as Debug, Release, RelWithDebInfo,and so on. Debug is convennient for developers. Details is shown in #547. In fact, Debug, Release, RelWithDebInfo are all good choices.