dev-lang/ghc-7.6.3-r1: disable ghci relinking hack on prefix

We can't sanely control glibc's contents on prefix,
like on RHEL5 with glibc-2.7 as found out by Wilfred.

Just disable it there.

Reported-by: Wilfred Hughes
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>