Everything is ok. If the second argument of AS_IF does not include any
executable commands, it is perfectly acceptable and generates valid
code because AS_IF uses : command immediatelly after "then" keyword.
./configure: line 1670: syntax error near unexpected token `fi'
./configure: line 1670: `fi'
$ cat ./configure | tail -n 10
if true; then :
# Another comment
You see, generated code is not correct: there is no command in "else"
part, bash does not like it.
It is not a big problem, but it is quite confusing for newbie user. And
it seems it can be easily avoided by generating ":" command in the
"else" part, like AS_IF does it in "then" part of conditional