Enabling Developer Toolset 7 for Jenkins' lo_callgrind_linux

...aka "Callgrind Linux", <https://ci.libreoffice.org/job/lo_callgrind_linux/>

Change-Id: I518e579ec4ca7b36f700ed412d86feef37c3e203
diff --git a/distro-configs/Jenkins/PerfSuite_Linux.conf b/distro-configs/Jenkins/PerfSuite_Linux.conf
index fcb6009..504ee92 100644
--- a/distro-configs/Jenkins/PerfSuite_Linux.conf
+++ b/distro-configs/Jenkins/PerfSuite_Linux.conf
@@ -6,3 +6,5 @@
--disable-ccache
--enable-symbols
--enable-mergelibs
CC=/opt/rh/devtoolset-7/root/usr/bin/gcc
CXX=/opt/rh/devtoolset-7/root/usr/bin/g++