esp8266/tools/sdk/lib/README.md

Updating SDK libraries

• Copy .a files from SDK lib directory to this directory
• Run fix_sdk_libs.sh

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