gas: sparc: fix relaxation of CALL instruction into branches in a.out targets

gas: sparc: fix relaxation of CALL instruction into branches in a.out targets

This patch avoids CALL instructions to be optimized into branches if
the symbols referred to in the CALL instruction are not fully resolved
at the time the assembler writes its output.

Tested in sparc64-linux-gnu and sparc-sun-sunos4.1.3 targets.
No regressions.

gas/ChangeLog:

2017-04-25  Jose E. Marchesi  <jose.marchesi@oracle.com>

	PR gas/21407
	* config/tc-sparc.c (md_apply_fix): Do not transform `call'
	instructions into branch instructions in fixups generating
	additional relocations.
	* testsuite/gas/sparc/call-relax.s: New file.
	* testsuite/gas/sparc/call-relax.d: Likewise.
	* testsuite/gas/sparc/call-relax-aout.d: Likewise.
	* testsuite/gas/sparc/sparc.exp: Test call-relax and call-relax-aout.