Fix incorrect use of FCL_BUILD_TYPE_DEBUG

[jslee02]

The build type check with FCL_BUILD_TYPE_DEBUG and FCL_BUILD_TYPE_RELEASE should be done using their values instead of whether they are defined or not since they are always defined.

[sherm1]

Change looks good.

Question: is it useful to have these macros in addition to the language-standard NDEBUG macro?

[jslee02]

Question: is it useful to have these macros in addition to the language-standard NDEBUG macro?

When I added those macros, I considered the case FCL would like to have more build types (e.g., BUILD_TYPE_RELWITHDEBINFO and BUILD_TYPE_MINSIZEREL) with different behaviors, but haven't found any use case so far. I'm not against removing them.

[sherm1]

Could be a topic for a different PR.