[Buildroot] how to install package ltp-testsuite outside of target directory

[YUAN Linyu]

Hi,

When I build ltp-testsuite into a ARM initramfs image, it's very big, 
so system can't load module which can load without ltp-testsuite built.

section 3 reloc 1 sym 'vmalloc_to_page': relocation 28 out of range
 (0xbf000034 -> 0xc1a18f1c)

I try to build ltp-testsuite outside the target rootfs.,
for example, $(BASE_DIR)/ ltp-testsuite, 
it need change below configuration in pkg-autotools.mk,
and add one configuration item to enable user define a directory for install.

$(2)_INSTALL_TARGET_OPTS                ?= DESTDIR=$$(TARGET_DIR) install
==>
$(2)_TARGET_DIR		?= $$(TARGET_DIR)
$(2)_INSTALL_TARGET_OPTS                ?= DESTDIR=$$($(2)_TARGET_DIR) install

anyone have a better solution?

thanks