libgfortran: Partly revert my r12-6498 change to fix Solaris build [PR104006]

libgfortran: Partly revert my r12-6498 change to fix Solaris build [PR104006]

In r12-6498 I've added $(version_dep) to BUILT_SOURCES, previously version_dep
on Linux used to be a file in $(srcdir), but with my changes it is a generated
file in the object directory (preprocessed version of the $(srcdir) file)
and I thought generated files belong to BUILT_SOURCES so that they are
cleaned up etc.
For Linux that is fine, but it broke parallel builds on Solaris.
BUILT_SOURCES is a special variable for automake where automake ensures
that for make all, make check and make install all those $(BUILT_SOURCES)
are generated before actually starting building in parallel the various
object files.  That way we can avoid hacks like:
$(patsubst %.F90,%.lo,$(notdir $(filter %.F90,$(prereq_SRC)))): kinds.inc c99_protos.inc
$(patsubst %.c,%.lo,$(notdir $(filter %.c,$(prereq_SRC)))): kinds.h
$(patsubst %.f90,%.lo,selected_real_kind.f90): selected_real_kind.inc
$(patsubst %.f90,%.lo,selected_int_kind.f90): selected_int_kind.inc
$(patsubst %.F90,%.lo,ieee_exceptions.F90): fpu-target.inc
$(patsubst %.F90,%.lo,ieee_arithmetic.F90): fpu-target.inc ieee_exceptions.lo
$(patsubst %.c,%.lo,fpu.c): fpu-target.h
which makes those dependencies explicit but hides it from automake, so that it
doesn't throw away its rules for those object files.
On Solaris, $(version_dep) contains gfortran.ver and gfortran.ver-sun.
gfortran.ver is like on Linux, it can be in $(BUILT_SOURCES), but unfortunately
gfortran.ver-sun depends on all the object files being compiled already,
so if gfortran.ver-sun appears in $(BUILT_SOURCES), the BUILT_SOURCES function
of ensuring the generated files are generated before building object files
is gone, almost everything is built before all-am is entered and there
are no explicit dependencies that e.g. *.F90 files depend on
kinds.inc etc.

So, this change reverts that mistake and instead adds $(version_dep) to
what is removed during make clean (clean-local in particular).

2022-01-14  Jakub Jelinek  <jakub@redhat.com>

	PR libfortran/104006
	* Makefile.am (BUILT_SOURCES): Don't include $(version_dep).
	(clean-local): Remove $(version_dep).
	* Makefile.in: Regenerated.