Impeach||GTFO 
The eschaton can't happen until I understand when to add square brackets in configure.ac. It's one of those weird things in Revelations.
Seriously, it looks like you just add square brackets when in doubt, add double square brackets
QUOTIE QUOTE QUOTE QUOTEQUOTE
"since autoconf generates shell code, you often want to output shell variable expansion, rather than performing M4 parameter expansion. To do this, you must use M4 quoting to separate the ‘$’ from the next character in the definition of your macro. If the macro definition occurs in single-quoted text, then insert another level of quoting; if the usage is already inside a double-quoted string, then split it into concatenated strings."
AAAAAAAAAAAAAAAAAAAH
DAMMIT VERN I TOLD YOU WE DON'T UNDERSTAND ALL THIS QUOTING SHIT