Small improvements to llvm demo page (Bug 1440)

Hi,

Some time ago I posted a patch against Bug 1440
<http://llvm.org/bugs/show_bug.cgi?id=1440> about adding a compiler
and target option to the llvm demo page. I didn't get any response
when fixing the last problems in the patch. Will anyone take a look at
it?

The patch adds a compiler option with the choice of clang and
llvm-gcc. The source languages C/C++/Obj-C/Obj-C++ are available from
clang and C/C++/Fortran is available from llvm-gcc. An auto-generated
target option is provided. The list is read from `llc -version` and
split in two groups: Stable targets and Experimental targets. Maybe
"stable" is too much, fx. I read the C Backend is not that well
supported anymore. Special targets (always listed first) are LLVM
assembly (provided by llvm-dis) and LLVM C++ API code. At last but not
least the shown version number is taken from `llvm-config --version`.

Any comments appreciated.

Thanks,
Bjarke Walling