parallel make potential problem in bfd/doc

[Dan Nicolaescu]

Hi,

It looks like the bfd/doc directory might have problems with parallel
make if files need to be updated.

Rules for updating the texi files look like this:

aoutx.texi: chew.c $(srcdir)/../aoutx.h $(srcdir)/doc.str
        $(MAKE) $(MKDOC)
        ./$(MKDOC) -f $(srcdir)/doc.str <$(srcdir)/../aoutx.h >aoutx.tmp
        $(SHELL) $(srcdir)/../../move-if-change aoutx.tmp aoutx.texi

archive.texi: chew.c $(srcdir)/../archive.c $(srcdir)/doc.str
        $(MAKE) $(MKDOC)
        ./$(MKDOC) -f $(srcdir)/doc.str <$(srcdir)/../archive.c >archive.tmp
        $(SHELL) $(srcdir)/../../move-if-change archive.tmp archive.texi


say doc.str is new, that will make all the rules for the .texi files run
"$(MAKE) $(MKDOC)" in parallel. This is wasteful to start with.  
It's also not impossible that 2 different makes try to write the binary
at the same time...