scripts/functions: add a generic custom location infrastructure

Add a generic custom location infrastructure (inspired by the one in
kernel/linux) to allow the user to use custom tarballs or directories
for any component.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
[yann.morin.1998@free.fr: move config option, improve help text, fix API doc]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <131c163c69f9cc81d2be.1349931191@localhost.localdomain>
PatchWork-Id: 190784
Message-Id: <0bbaba9190a76ba97f72.1349931192@localhost.localdomain>
PatchWork-Id: 190785

--- a/bfd/elf32-arm.c

+++ b/bfd/elf32-arm.c

@@ -12408,7 +12408,8 @@ elf32_arm_check_relocs (bfd *abfd, struc

 	  /* If the symbol is a function that doesn't bind locally,

 	     this relocation will need a PLT entry.  */

-	  root_plt->refcount += 1;

+	  if (root_plt->refcount != -1)

+	    root_plt->refcount += 1;

 	  if (!call_reloc_p)

 	    arm_plt->noncall_refcount++;