This commit teaches CMake about the g95 compiler from
http://www.g95.org
We use 'G95' as the compiler id string, and add some basic flags.
See issue #9241.
IBM rebranded its VisualAge compiler to XL starting at version 8.0. We
use the compiler id "XL" for newer versions and "VisualAge" for older
versions. We now also recognize the "z/OS" compiler, which is distinct
from XL.
Some SGI compilers define _SGI_COMPILER_VERSION in addition to the old
_COMPILER_VERSION preprocessor symbol. It is more distinctive, so we
should check it in case the old one is ever removed.
The SGI preprocessor /usr/lib/cpp produces bad output on this code:
#if 1
A
#elif 1
B
#else
C
#endif
Both 'A' and 'C' appear in the output! We work around the problem by
using '#elif 1' instead of '#else'.
This fixes detection of the SGI Fortran compiler id in -o32 mode.
This enhances the Fortran compiler id detection by using a source that
can compile either as free or fixed format. As long as the compiler
knows it should preprocess the source file (.F) the identification can
work. Even free-format compilers may try fixed-format parsing if the
user specifies certain flags, so we must support both.
