Remove symbols defined in abi.cpp from libstdc++

tools/sdk/lib/README.md

@@ -8,3 +8,17 @@ After updating SDK libraries to a new version, do the following changes.
     ```bash
     xtensa-lx106-elf-ar -d libmain.a mem_manager.o
     ```
+
+## Updating libstdc++
+
+After building gcc using crosstool-NG, get compiled libstdc++ and remove some objects:
+
+    xtensa-lx106-elf-ar d libstdc++.a pure.o
+    xtensa-lx106-elf-ar d libstdc++.a vterminate.o
+    xtensa-lx106-elf-ar d libstdc++.a guard.o
+    xtensa-lx106-elf-ar d libstdc++.a functexcept.o
+    xtensa-lx106-elf-ar d libstdc++.a del_op.o
+    xtensa-lx106-elf-ar d libstdc++.a del_opv.o
+    xtensa-lx106-elf-ar d libstdc++.a new_op.o
+    xtensa-lx106-elf-ar d libstdc++.a new_opv.o
+