esp32s2: remove -nostdlib accidentally added

-nostdlib was removed in 9a2af7a and then accidentally added
in 1c2cc54.

The issue manifested itself as a failure to link some symbols from
libgcc, even though libgcc should implicitly appear at the end of the
linker command line when -nostdlib is not given.

tools/cmake/toolchain-esp32s2.cmake

@@ -4,6 +4,5 @@ set(CMAKE_C_COMPILER xtensa-esp32s2-elf-gcc)
 set(CMAKE_CXX_COMPILER xtensa-esp32s2-elf-g++)
 set(CMAKE_ASM_COMPILER xtensa-esp32s2-elf-gcc)
 
-set(CMAKE_EXE_LINKER_FLAGS "-nostdlib" CACHE STRING "Linker Base Flags")
 set(CMAKE_C_FLAGS "-mlongcalls" CACHE STRING "C Compiler Base Flags")
 set(CMAKE_CXX_FLAGS "-mlongcalls" CACHE STRING "C++ Compiler Base Flags")