boot/espressif/tools/toolchain-esp32.cmake

set(CMAKE_SYSTEM_NAME Generic)

set(CMAKE_C_COMPILER xtensa-esp32-elf-gcc)
set(CMAKE_CXX_COMPILER xtensa-esp32-elf-g++)
set(CMAKE_ASM_COMPILER xtensa-esp32-elf-gcc)
set(_CMAKE_TOOLCHAIN_PREFIX xtensa-esp32-elf-)

set(CMAKE_C_FLAGS "${UNIQ_CMAKE_C_FLAGS}" CACHE STRING "C Compiler Base Flags" FORCE)
set(CMAKE_CXX_FLAGS "${UNIQ_CMAKE_CXX_FLAGS}" CACHE STRING "C++ Compiler Base Flags" FORCE)
set(CMAKE_ASM_FLAGS "${UNIQ_CMAKE_ASM_FLAGS}" CACHE STRING "ASM Compiler Base Flags" FORCE)

set(CMAKE_EXE_LINKER_FLAGS "-Wl,--gc-sections" CACHE STRING "Linker Base Flags")