CTFE formatting of floating point values

[Johannes Pfau]

I think this is a known issue:
DMD expects real.stringof to return a string in the %g format. However
the GCC function used for formatting real numbers always returns the %e
format.

There is a failing test for this in the test suite. (runnable/test42.d
(test49)). Would it be OK to disable this test if a file a bug
report on our bugtracker and on the gcc bugtracker? This would
allow running the other tests in that file.