Merge branch 'feature/ccache' into 'master'

Optimize compile builds using ccache and gold linker

See merge request !122

cmake/modules/AmdisMacros.cmake

 include(AmdisCXXFeatures)
 include(AddAmdisExecutable)
 
+# some optimization of the compile times
+find_program(CCACHE_PROGRAM ccache)
+if (CCACHE_PROGRAM)
+  set(CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE_PROGRAM}")
+endif ()
+
+if (UNIX AND NOT APPLE)
+  execute_process(COMMAND ${CMAKE_C_COMPILER} -fuse-ld=gold -Wl,--version ERROR_QUIET OUTPUT_VARIABLE ld_version)
+  if ("${ld_version}" MATCHES "GNU gold")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=gold -Wl,--disable-new-dtags")
+  endif()
+endif()
+
+
 if (NOT BACKEND)
   set(BACKEND "ISTL" CACHE STRING "LinearAlgebra backend. One of MTL, EIGEN, PETSC, ISTL")
   set_property(CACHE BACKEND PROPERTY STRINGS "MTL" "EIGEN" "ISTL" "PETSC")