Fix silicon by adding the gcc-6 dependency.

toolset/setup/linux/frameworks/silicon.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-fw_depends clang-3.8
+fw_depends clang-3.8 gcc-6
 
 RETCODE=$(fw_exists ${IROOT}/silicon.installed)
 [ ! "$RETCODE" == 0 ] || { \

toolset/setup/linux/systools/gcc-6.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+
+RETCODE=$(fw_exists ${IROOT}/gcc-6.installed)
+[ ! "$RETCODE" == 0 ] || { \
+  source $IROOT/gcc-6.installed
+  return 0; }
+
+sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+sudo apt-get -yq update
+sudo apt-get install -qqy gcc-6
+
+touch $IROOT/gcc-6.installed