Sorry to be that guy, but what's an LTS compiler? (Google was not forthcoming.)
http://en.wikipedia.org/wiki/Long-term_support
The basic idea is that once released, the LTS version of the compiler would continue to receive fixes and updates for several years (at least two according to Wikipedia), no matter how many new versions are released during that time.
Good luck with that. I tried to go on with the Ubuntu's LTS once, and the logic definitely doesn't work. Bugs, even major ones, just pile up faster than the remaining couple developers can fix, and it's was too painful of an experience to repeat. Ubuntu LTS has shelf life of 6-12 months unless if you start paying. Which is unfortunate.
So you want something for nothing. Why exactly would Ubuntu (or anybody else) want you as an user?
Yep. I see this a lot in the scientific world. Clusters and other high-performance hardware run old versions of Scientific Linux or CentOS (because they are well-supported and the bugs are known). However, a lot of open source project (e.g. in machine learning) expect you to run the latest Ubuntu or OS X version. Result: you usually end up hand-compiling large amounts of software, manually adding '-I' and '-L' flags to oddball build systems that don't pick up CFLAGS or LDFLAGS correctly.
Nobody cares about backwards compatibility, everyone wants the new toys.