message: Use gold linker if found when building on Linux
  Also add --gdb-index flag when using gold linker
diff: @@ -41,12 +41,20 @@ ifneq ($(COMPILER),clang)
  WARNINGS += -Wsuggest-attribute=format -Wimplicit-fallthrough=2
  endif
  +# Investigate: Improving C++ Builds with Split DWARF
  +# http://www.productive-cpp.com/improving-cpp-builds-with-split-dwarf/
  +
  CFLAGS = $(WARNINGS) -march=native -fno-exceptions -gdwarf-4 -g2 $(SDL2FLAGS) $(GTK3FLAGS) -I/usr/include/freetype2
  CFLAGS += -DUSE_FREETYPE -D_LARGEFILE64_SOURCE=1 -D_FILE_OFFSET_BITS=64
  CXXFLAGS = -fno-rtti -Woverloaded-virtual -Wno-class-memaccess
  LDFLAGS = -march=native -gdwarf-4 -g2 -Wl,--build-id=sha1
  LIBS = -Wl,--no-as-needed -lm -ldl -lpthread -lfreetype -lstdc++ $(SDL2LIBS)
  +ifneq ("$(wildcard /usr/bin/ld.gold)","")
  + $(info Using gold linker...)
  + LDFLAGS += -fuse-ld=gold -Wl,--gdb-index
  +endif
  +
  # https://gcc.gnu.org/onlinedocs/libstdc++/manual/profile_mode.html#manual.ext.profile_mode.intro
  # To resolve addresses from libstdcxx-profile.conf.out: addr2line -C -f -e _debug/gpuvis 0x42cc6a 0x43630a 0x46654d
  # CFLAGS += -D_GLIBCXX_PROFILE -D_GLIBCXX_PROFILE_CONTAINERS
  