[mythtv] New configure script oddities

[Anduin Withers]

> FYI - I had trouble compiling with the new configure script on my
> machine, I get:

Yeah, some sections are on the border where certain compiler flags will
deplete the number of registers to the point where the code won't compile.
There isn't much the configure script can do to work around this.

However there are other oddities that I'd like to get worked out as well
(like --extra-cflags; it actually modifies OPTFLAGS, and OPTFLAGS is only
used in release mode, there is a good reason OPTFLAGS isn't used for debug
mode but currently it means you can pass extra CFLAGS in debug mode). Also
for release mode QMAKE_CFLAGS_RELEASE=QMAKE_CXXFLAGS_RELEASE, for debug mode
a similar QMAKE_CFLAGS_DEBUG=QMAKE_CXXFLAGS_DEBUG isn't done.

Overall though I like the new configure script, it just needs a little
playing with.

-- 
Anduin Withers