[lldb][test] When an external stdlib is specified do not link to the system stdlib (llvm#164462)

On linux if you specify the an external libc++ and clang will still link
to the system's libc++. This patch fixes that.

Fixes llvm#116040

(cherry picked from commit ec55aa4)

Author: da-viper

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

@@ -387,7 +387,9 @@ ifeq (,$(filter 1, $(USE_LIBSTDCPP) $(USE_LIBCPP) $(USE_SYSTEM_STDLIB)))
     ifneq "$(LIBCPP_INCLUDE_TARGET_DIR)" ""
       CXXFLAGS += -cxx-isystem $(LIBCPP_INCLUDE_TARGET_DIR)
     endif
-    LDFLAGS += -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
+
+	# If `-nostdlib++` is not passed, clang will link to the system's stdlib.
+    LDFLAGS += -nostdlib++ -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
   else
     USE_SYSTEM_STDLIB := 1
   endif
@@ -408,7 +410,8 @@ ifeq (1,$(USE_LIBCPP))
 		ifneq "$(LIBCPP_INCLUDE_TARGET_DIR)" ""
 				CXXFLAGS += -cxx-isystem $(LIBCPP_INCLUDE_TARGET_DIR)
 		endif
-		LDFLAGS += -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
+		# If `-nostdlib++` is not passed, clang will link to the system's stdlib.
+		LDFLAGS += -nostdlib++ -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
 	else
 		ifeq "$(OS)" "Android"
 				# Nothing to do, this is already handled in