Default CMake build type

[dnadlinger]

As reported by @Safety0ff, apparently CMake defaults to some sort of unoptimized build (also see #539 (comment)). I have never stumbled upon this, as LLVM leaks -O3 -fomit-frame-pointer into the llvm-config output, at least when it is built with CMake, thus also enabling optimizations.

We should make sure that we build an optimized version by default if the user specifies no build type. @Safety0ff, could you please post some details on your system config (OS, CMake version, how you built/installed LLVM)?

Note that we might run into trouble if we just set CMAKE_BUILD_TYPE to Release by default, as this defines NDEBUG, which requires a matching LLVM build.

[Trass3r]

That problem needs to be solved anyway.
Currently I just undefine NDEBUG locally but a proper solution would be nice.

[Safety0ff]

RelWithDbgInfo minus NDEBUG would probably be a good choice.
I'm using gentoo with cmake 2.8.12.2 and llvm 3.4.1 (both install via portage.) After git clone'ing ldc I did:

mkdir build && cd build && cmake ..

Which defaults to empty CXX_FLAGS
When writing CMake scripts I usually add a check to see if a variable is unset, then use the default, but only if it is the first configuration run (using a hidden cached variable to mark the end of the first configuration run.)

[Trass3r]

Well on Linux RelWithDebInfo results in huge executables and memory consumption during compilation, at least for clang.

[Trass3r]

http://llvm.org/bugs/show_bug.cgi?id=14885