bfd: xtensa: fix callx relaxation

bfd: xtensa: fix callx relaxation

Big section alignment requirements between source and destination of a
long call can result in making call range bigger than what's reachable
by the call opcode. Add biggest section alignment of sections between
the call site and call destination to the call distance when making
long call relaxation decision.

2019-02-20  Eric Tsai  <erictsai@cadence.com>
bfd/
	* elf32-xtensa.c (is_resolvable_asm_expansion): Scan output
	sections between the call site and call destination and adjust
	call distance by the largest alignment.

ld/
	* testsuite/ld-xtensa/call_overflow.d: New test definition.
	* testsuite/ld-xtensa/call_overflow1.s: New test source.
	* testsuite/ld-xtensa/call_overflow2.s: New test source.
	* testsuite/ld-xtensa/call_overflow3.s: New test source.
	* testsuite/ld-xtensa/xtensa.exp: Add call_overflow test.