Generate cppcheck suppressions based on ENABLE_MANTIDPLOT

If the flag is off then some suppressions don't get matched
and then cppcheck warns of unmatched suppressions

buildconfig/CMake/CppCheckSetup.cmake

@@ -5,7 +5,11 @@ if ( CPPCHECK_EXECUTABLE )
   # We must export the compile commands for cppcheck to be able to check
   # everything correctly
   set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
-
+  if(ENABLE_MANTIDPLOT)
+    set(MANTIDPLOT_CPPCHECK_SUPPRESSIONS "*:${CMAKE_SOURCE_DIR}/MantidPlot/src/zlib123/*
+*:${CMAKE_SOURCE_DIR}/MantidPlot/src/origin/tree.hh
+*:${CMAKE_SOURCE_DIR}/MantidPlot/src/nrutil.cpp")
+  endif()
   configure_file(${CMAKE_SOURCE_DIR}/buildconfig/CMake/CppCheck_Suppressions.txt.in ${CMAKE_BINARY_DIR}/CppCheck_Suppressions.txt)
 
   # setup the standard arguments

buildconfig/CMake/CppCheck_Suppressions.txt.in

@@ -45,8 +45,6 @@ syntaxError:${CMAKE_SOURCE_DIR}/Framework/API/src/MatrixWorkspace.cpp
 
 // Mantid Plot specific ones we probably won't fix before removal
 
-*:${CMAKE_SOURCE_DIR}/MantidPlot/src/origin/tree.hh
-*:${CMAKE_SOURCE_DIR}/MantidPlot/src/nrutil.cpp
 
 pureVirtualCall:${CMAKE_SOURCE_DIR}/qt/scientific_interfaces/Indirect/IndirectBayesTab.cpp
 pureVirtualCall:${CMAKE_SOURCE_DIR}/qt/scientific_interfaces/Indirect/IndirectBayesTab.h
@@ -95,4 +93,4 @@ noCopyConstructor:${CMAKE_SOURCE_DIR}/Framework/Geometry/inc/MantidGeometry/Rend
 *:${CMAKE_SOURCE_DIR}/Framework/ICat/src/GSoap/*
 *:${CMAKE_SOURCE_DIR}/Framework/ICat/src/ICat3/GSoapGenerated/*
 *:${CMAKE_SOURCE_DIR}/Framework/ICat/src/ICat4/GSoapGenerated/*
-*:${CMAKE_SOURCE_DIR}/MantidPlot/src/zlib123/*
+${MANTIDPLOT_CPPCHECK_SUPPRESSIONS}