feat: add lld linker

docs/whole-program-llvm.md

@@ -5,9 +5,13 @@ When applying analysis, we usually need to work on a `linked` LLVM bitcode file,
 # using `llvm-link`
 This requires each step of compilation to generate `bc` files and then apply `llvm-link` against all `bc` files.
 
-# using `gold link`
+# using `lld linker`
 Adding flags `-flto -fuse-ld=lld -Wl,-save-temps` to generate the temporal bc files.
 
+# using `gold linker`
+`export LDFLAGS="-flto -fuse-ld=gold -Wl,-plugin-opt=emit-llvm"`
+http://gbalats.github.io/2015/12/10/compiling-autotooled-projects-to-LLVM-bitcode.html
+
 # using `wllvm` or `gllvm`
 [wllvm](https://github.com/travitch/whole-program-llvm) and [gllvm](https://github.com/SRI-CSL/gllvm) are solutions to generating linked bitcode files.
 For example, when using gllvm, you should ensure the corresponding compiler is gclang and gclang++, which can be typically set by using `export CC=gclang CXX=gclang++`.