tools: bypass atomic instruction variant for esp32c6 temporarily

Current riscv32-esp-elf-gcc can't provide the atomic intrinsic
functions.

Bypass it for now. Will revert this commit when a new toolchain is
ready.

tools/cmake/toolchain-esp32c6.cmake

@@ -7,12 +7,12 @@ set(CMAKE_CXX_COMPILER riscv32-esp-elf-g++)
 set(CMAKE_ASM_COMPILER riscv32-esp-elf-gcc)
 set(_CMAKE_TOOLCHAIN_PREFIX riscv32-esp-elf-)
 
-remove_duplicated_flags("-march=rv32imac ${CMAKE_C_FLAGS}" UNIQ_CMAKE_C_FLAGS)
+remove_duplicated_flags("-march=rv32imc ${CMAKE_C_FLAGS}" UNIQ_CMAKE_C_FLAGS)
 set(CMAKE_C_FLAGS "${UNIQ_CMAKE_C_FLAGS}" CACHE STRING "C Compiler Base Flags" FORCE)
-remove_duplicated_flags("-march=rv32imac ${CMAKE_CXX_FLAGS}" UNIQ_CMAKE_CXX_FLAGS)
+remove_duplicated_flags("-march=rv32imc ${CMAKE_CXX_FLAGS}" UNIQ_CMAKE_CXX_FLAGS)
 set(CMAKE_CXX_FLAGS "${UNIQ_CMAKE_CXX_FLAGS}" CACHE STRING "C++ Compiler Base Flags" FORCE)
 
-remove_duplicated_flags("-nostartfiles -march=rv32imac --specs=nosys.specs \
+remove_duplicated_flags("-nostartfiles -march=rv32imc --specs=nosys.specs \
                         ${CMAKE_EXE_LINKER_FLAGS}"
                         UNIQ_CMAKE_SAFE_EXE_LINKER_FLAGS)
 set(CMAKE_EXE_LINKER_FLAGS "${UNIQ_CMAKE_SAFE_EXE_LINKER_FLAGS}" CACHE STRING "Linker Base Flags" FORCE)