ARC: Fix ld/pr24511 test

ARC: Fix ld/pr24511 test

With this patch, ld/pr24511 test passes for ARC.

At first glance, the test was failing because the order of
"__init_array_start" and "__fini_array_start" weak symbols were
reversed:

$ nm -n dump.out

      expected output          |          real output
00002104 D __init_array_start  |  00002104 D __fini_array_start
0000210c D __fini_array_start  |  00002104 D __init_array_start

The order of the symbols are different as a side effect of both
symbols being mapped to the _same_ address (0x2104).  Looking
further into the mapping logs [1] revealed that the linker
script must consider all instances of ".init_array" (in other
words ".init_array.*") inside its relevant section. Same logic
holds for ".fini_array".

Therefore, adding "KEEP (*(SORT(.init_array.*)))" to the linker
script, along with the one for ".finit_array.*", resolved the
problem.  While at it, I took the liberty of refactoring the
script a little bit and made those pieces of script macros.

[1] Linker's mapping for the relevant part of the test
---------------------------------------------------------------
.init_array     0x2104        0x0
                0x2104        PROVIDE (__init_array_start = .)
 *(.init_array)
                [!provide]    PROVIDE (__init_array_end = .)

.fini_array     0x2104        0x0
                0x2104        PROVIDE (__fini_array_start = .)
 *(.fini_array)
                [!provide]    PROVIDE (__fini_array_end = .)

.data           0x2104        0x0
 *(.data .data.* .gnu.linkonce.d.*)
 .data          0x2104        0x0 pr24511.o

.init_array.01000
                0x2104        0x8
 .init_array.01000
                0x2104        0x8 pr24511.o

.fini_array.01000
                0x210c        0x8
 .fini_array.01000
                0x210c        0x8 pr24511.o
---------------------------------------------------------------

ld:
	* scripttempl/elfarc.sc (.init_array): Keep ".init_array.*".
	  (.fini_array): Keep ".fini_array.*".

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>