FCLINK with conditional fortran sources

[Christopher Hulbert]

I have a library that has an optional fortran interface. I'd rather
not separate this into two different libraries, but on systems without
a fortran compiler, FCLD is empty and creating a libtool archive
fails. Is there another way around this. My Makefile.am is something
like

liba_la_SOURCES = a.c

if FORTRAN
liba_la_SOURCES += b.f90
endif