Only link default native backend by default.

Use the new option --add-backend to link in additional targets.

premake.lua

@@ -5,6 +5,13 @@ project.name = llvmdc
 -- we always make vtables opaque, it simply kills performance...
 OPAQUE_VTBLS = 1
 
+-- enables additional backends
+addoption("add-backend", "Link in more than the native LLVM backend")
+EXTRA_BACKENDS=""
+if options["add-backend"] then
+    EXTRA_BACKENDS=options["add-backend"]
+end
+
 -- use of boehm gc
 USE_BOEHM_GC = 0
 if OS ~= "windows" then
@@ -55,7 +62,7 @@ package.excludes = { "dmd/idgen.c", "dmd/impcnvgen.c" }
 package.buildoptions = { "-x c++", "`llvm-config --cxxflags`" }
 package.linkoptions = {
     -- long but it's faster than just 'all'
-    "`llvm-config --libs core asmparser bitreader bitwriter linker support target transformutils scalaropts ipo instrumentation x86 powerpc`",
+    "`llvm-config --libs backend asmparser bitreader bitwriter linker ipo instrumentation " .. EXTRA_BACKENDS .. "`",
     "`llvm-config --ldflags`",
 }
 package.defines = {