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

diff -dur uClibc-0.9.28.1.orig/libc/sysdeps/linux/common/Makefile uClibc-0.9.28.1/libc/sysdeps/linux/common/Makefile

--- uClibc-0.9.28.1.orig/libc/sysdeps/linux/common/Makefile	2007-01-26 00:54:19.000000000 +0100

+++ uClibc-0.9.28.1/libc/sysdeps/linux/common/Makefile	2007-02-01 08:44:37.000000000 +0100

@@ -25,6 +25,10 @@

 SRCS := $(filter-out sbrk.c,$(SRCS))

 endif

+ifneq ($(strip $(UCLIBC_HAS_LFS)),y)

+SRCS := $(filter-out readahead.c,$(SRCS))

+endif

+

 ifneq ($(strip $(UCLIBC_HAS_SSP)),y)

 SRCS := $(filter-out ssp.c,$(SRCS))

 endif