[patch] Install libgfortranbegin.a as compiler library instead of system library

[DJ Delorie]

I'm not that familiar with libfortran, but...

gcc installs libgcc.a and crtbegin.o like this:

	$(INSTALL_DATA) ./libgcc.a $(DESTDIR)$(libsubdir)/
	$(INSTALL_DATA) crtbegin.o $(DESTDIR)$(libsubdir)/

The install path needs to take into account two things:

1. DESTDIR must be supported, so that the toolchain can be installed
   into an alternate tree, and

2. The multilib subdir must be accomodated.

I think it's OK for libfortranbegin.a to be installed wherever
libgcc.a is installed, just make sure those two items are supported in
the final Makefile.