[Ada] No error on missing enclosing parentheses in Expression Function

[Ada] No error on missing enclosing parentheses in Expression Function

This patch fixes an issue whereby an expression within an expression
function declaration or completion without proper parenthesization is
incorrectly accepted by the compiler.

2018-01-11  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* par-ch6.adb (Scan_Body_Or_Expression_Function): Add additional check
	to make sure a given expression function is properly parenthesized.

gcc/testsuite/

	* gnat.dg/expr_func4.adb: New testcase.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@256517 138bc75d-0d04-0410-961f-82ee72b054a4