Preserve user-passed CXXFLAGS with --enable-debug

[gavinandresen]

I was surprised that this didn't work:
./configure --enable-debug CXXFLAGS="-DDEBUG_LOCKORDER"

@theuni : I don't THINK this will have unintended consequences, is there a reason --enable-debug overwrote CFLAGS/CXXFLAGS?

[theuni]

@gavinandresen looks good to me, agreed that the behavior is unexpected. A few thoughts, though:

• I believe it's that way because "-O2 -g" are already added by default. After this change, a ./configure --enable-debug will end up with duped flags I think. Not a problem really, the last flag wins.
• You really want to be passing that in as CPPFLAGS=-DDEBUG_LOCKORDER anyway. Those are pre-processor flags, which exist separately so they don't get mixed up in arguments about optim flags and etc.
• IMO There should be no need to pass -DDEBUG_LOCKORDER via a flag, that kinda defeats the purpose of having configure options to begin with. How about just adding -DDEBUG_LOCKORDER to CPPFLAGS in the --enable-debug case?

[gavinandresen]

RE: CPPFLAGS: hmm, then --enable-debug should add -DDEBUG to CPPFLAGS instead of CFLAGS/CXXFLAGS...

RE: adding -DDEBUG_LOCKORDER to --enable-debug: sounds good to me.

[laanwj]

How about just adding -DDEBUG_LOCKORDER to CPPFLAGS in the --enable-debug case?

Sounds good to me.

Although maybe then it should be documented then that the flag doesn't just add debug information, but also enables specific debug functionality.

Or maybe that's already clear:

--enable-debug          use debug compiler flags and macros (default is no)

[gavinandresen]

Tweaked based on comments:

Three changes to how configure --enable-debug behaves:

1. Preserve user-passed CXXFLAGS/CFLAGS
2. Compile with -DDEBUG_LOCKORDER
3. Add -DDEBUG -DDEBUG_LOCKORDER to CPPFLAGS (since they are preprocessor options)

[theuni]

Thanks, looks good.