Haiku: fix configure C++ error message with -std=c++11

[AliceLR]

In my current Haiku (R1 beta 5) environment, configure will append -std=c++11 to CXX. The CXX check for BeOS/Haiku uses which "$CXX", which breaks when CXX contains options. I got rid of the quotes and switched it to command -v instead.

This has not been verified on actual BeOS, so if possible, please test that (I'm not aware how to, currently). edit: it's supposed to have Bash, but unclear if it's a version that supports -v?

Closes #78.

[sezero]

Is that command thing haiku specific? My linux bash doesn't know anything about it.

Do we have to verify CXX existence, btw? Why not just remove that check? Seems overzealous.

[sezero]

Is that command thing haiku specific? My linux bash doesn't know anything about it.

Agh, nevermind, seems like I tested wrong. This is OK.

[AliceLR]

Is that command thing haiku specific? My linux bash doesn't know anything about it.

-v for the command utility is POSIX but it was optional in 2004 and only mandatory as of 2008. I assume Bash had it long before that, but who knows... it's still technically more portable than which though (and doesn't get upset about the extra option like which does). 🙂

Do we have to verify CXX existence, btw? Why not just remove that check? Seems overzealous.

We might be able to replace it with AC_LANG(C++) or something, which it looks like I'm going to have put somewhere to detect B_AUDIO_INT anyway (they did not provide actual defines for these in media/MediaDefs.h...). Another odd thing about this driver: xmp is defining its own copies of B_AUDIO_CHAR and B_AUDIO_SHORT (and ignoring B_AUDIO_UCHAR and the libxmp unsigned flag). As far as I can tell, media/MediaDefs.h is supposed to be present in BeOS. I don't understand why it's doing this.

edit: actually, it looks like B_AUDIO_UCHAR and B_AUDIO_INT are from BeOS, so I don't have to do that autoconf modification (B_AUDIO_DOUBLE seems like the only Haiku-specific one). I think AC_LANG(C++) would still be fine though.