Update configure.ac scripts

[yadij]

Various cleanup changes to reduce the size of autoconf scripts and remove deprecated macros causing build warnings with autoconf v2.71.

[kinkie]

I can do that as soon as the build is fixed; from the output it looks like a typo snuck in

[yadij]

FTR, typo was the test condition on AS_IF cannot end with either CRLF or line wrap. Somehow yet to be determined is making the broken bit of shell script be unreachable with latest GCC and Debian unstable.

[kinkie]

@yadij , there's a couple of nits missing in configure.ac, then I'd say it's good to go

[rousskov]

I adjusted PR description, primarily to avoid leaving autoconf version hanging on its own line.