[Lapack] xLAMCH

[Jason Riedy]

And Sven Hammarling writes:
> My colleague, Mick Pont, has pointed out that we have already
> moved xLAMCH into the INSTALL directory, and so we could test
> for an IEEE machine at install time using the current xLAMCH
> and move a hard coded version into SRC if the machine
> parameters are IEEE.
It'll need to test which IEEE754 precisions correspond to REAL
and DOUBLE PRECISION as well.  Many compilers support command-
line flags to associate REALs of default kind with IEEE754
doubles.

Jason