How to create tests for FC?

[Ralf Wildenhues]

I am trying to put FC support in Libtool, and encounter a problem
similar and not quite orthogonal to Steven's suggestion for Automake[1].
Actually, more than one:

1) Within libtool.m4, a few tests need to be run to find out compiler/
linker characteristics.  These may give false failures if the user has
set AC_FC_SRCEXT(...) of AC_FC_FREEFORM differently than expected.
First: can I find out (without perusing Autoconf internal interface) if
they have been called, second may I override them and undo the effects
afterwards (how?) without harm, and third which would be the best choice
of extension for the test files if not?
Do I need to specify several source files for freeform/not-freeform?

2) For an eventual test suite addition, should I use `.f90' (so Automake
plays halfway well) and AC_FC_SRCEXT([.f90]), or stick fo `.f'?

Regards, and thanks for any help,
Ralf

FYI, some notes gathered (no guarantee on correctness):
- Intel ifc/ifort dislikes extension `.f95'.
- AIX xlf90/xlf95 dislikes extension that does not fit name.
- Some compilers decide freeform/language level based on extension,
  some on which name they are called by.
- Automake chooses $(F77) for `.f'.  Workaround?
- Automake needs to use $(FCFLAGS_$EXT) as mentioned in [1].  Wait for
  solving this or add to $(FCFLAGS) as workaround?
- Some compilers insist on either freeform or not and will reject the
  other one.

[1] http://lists.gnu.org/archive/html/automake/2005-06/msg00012.html