Warning of gcc bugs affecting kernel builds

[Ralf Baechle <ralf@xxxxxxxxxxxxxx>]

There are two gcc bugs which are having serious impact on the kernel.

  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54369
  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54494

Afaics the first one affects SPARC and MIPS in versions 4.5 ... 4.7.1
while the second one affects all architectures but is specific to
gcc 4.7.0 and 4.7.1.

  Ralf