Update llvm/clang/lld to a version from today

This allows using GNU binutils strip and objcopy on executables with
dwarf debug info linked by lld.

This also improves clang's handling of detecting known libraries
that override default libraries to link.

build-llvm.sh

@@ -37,13 +37,13 @@ fi
 if [ -n "$SYNC" ] || [ -n "$CHECKOUT" ]; then
     cd llvm
     [ -z "$SYNC" ] || git fetch
-    git checkout 27b0d8a7623cfc7f194675352362fc4a16d2273f
+    git checkout b79cc9e7eb39c60a1f51e185490ea177252687e0
     cd tools/clang
     [ -z "$SYNC" ] || git fetch
-    git checkout 0d65696b0e430a4078829ffea218c0fb04421dd5
+    git checkout 561a0afd9c46b4ca38b09ee5a4b8115394cd4917
     cd ../lld
     [ -z "$SYNC" ] || git fetch
-    git checkout f86124c33d0a97cfd636a050361a27c8b9459c2b
+    git checkout 7002cf666988fabf24198f8608c2f79277b5b96a
     cd ../../..
 fi