dev-lang/ghc: add a USE=shared to live ebuild

Switches ghc to build shared libraries by default
for experimental purposes.

Addresses Issue #216 (#216)

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

dev-lang/ghc/ghc-9999.ebuild

@@ -55,7 +55,7 @@ fi
 LICENSE="BSD"
 SLOT="0/${PV}"
 KEYWORDS=""
-IUSE="dph doc +ghcbootstrap ghcmakebinary llvm"
+IUSE="dph doc +ghcbootstrap ghcmakebinary llvm +shared"
 REQUIRED_USE="ghcbootstrap"
 
 RDEPEND="
@@ -374,6 +374,13 @@ src_configure() {
 		echo "GhcLibWays=${GHC_LIBRARY_WAYS}" >> mk/build.mk
 	fi
 
+	# Experimental code. Not enabled by default in GHC yet.
+	if use shared; then
+		echo "DYNAMIC_BY_DEFAULT=YES" >> mk/build.mk
+	else
+		echo "DYNAMIC_BY_DEFAULT=NO" >> mk/build.mk
+	fi
+
 	# This is only for head builds
 	perl boot || die "perl boot failed"