[binutils-gdb] evaluate_subexp_standard: Factor out OP_VAR_VALUE handling.

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT fe13dfecbf7d5a9ba3a5d9f52e33e0ddacb39bcc ***

Author: Pedro Alves <palves@redhat.com>
Branch: master
Commit: fe13dfecbf7d5a9ba3a5d9f52e33e0ddacb39bcc

evaluate_subexp_standard: Factor out OP_VAR_VALUE handling.

A following patch will want to call the new evaluate_var_value
function in another spot.

gdb/ChangeLog:
2017-09-04  Pedro Alves  <palves@redhat.com>

	* eval.c (evaluate_var_value): New function, factored out from ...
	(evaluate_subexp_standard): ... here.