Unset COMPONENT_ADD_INCLUDEDIRS in cxx component

[paulreimer]

to fix C++ warning from -Wmissing-include-dirs

Example warning, with -Wmissing-include-dirs but before this patch:

CXX /private/tmp/tmp_build/firmware/build/cxx/cxx_exception_stubs.o
cc1plus: warning: /private/tmp/tmp_build/firmware/esp-idf/components/cxx/include: No such file or directory [-Wmissing-include-dirs]

[paulreimer]

Also added declarations for __cxa_guard_ functions to fix a -Wmissing-declarations warning in de9cfac.

Example warning:

/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp: In function 'int __cxa_guard_acquire(__cxxabiv1::__guard*)':
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp:116:16: warning: no previous declaration for 'int __cxa_guard_acquire(__cxxabiv1::__guard*)' [-Wmissing-declarations]
 extern "C" int __cxa_guard_acquire(__guard* pg)
                ^
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp: In function 'void __cxa_guard_release(__cxxabiv1::__guard*)':
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp:171:17: warning: no previous declaration for 'void __cxa_guard_release(__cxxabiv1::__guard*)' [-Wmissing-declarations]
 extern "C" void __cxa_guard_release(__guard* pg)
                 ^
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp: In function 'void __cxa_guard_abort(__cxxabiv1::__guard*)':
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp:191:17: warning: no previous declaration for 'void __cxa_guard_abort(__cxxabiv1::__guard*)' [-Wmissing-declarations]
 extern "C" void __cxa_guard_abort(__guard* pg)
                 ^
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp: In function 'void __cxa_guard_dummy()':
/private/tmp/tmp_build/firmware/esp-idf/components/cxx/cxx_guards.cpp:214:17: warning: no previous declaration for 'void __cxa_guard_dummy()' [-Wmissing-declarations]
 extern "C" void __cxa_guard_dummy()

[paulreimer]

FYI with this PR, I am now able to compile all C++ within esp-idf (and my app code) with

-Wall \
-Wextra \
-Wno-format-nonliteral \
-Wmissing-declarations \
-Wmissing-include-dirs \
-Wformat=2 \
-Wmissing-format-attribute

which is pretty nice!

[projectgus]

Very nice, Paul! We should add some of these to our CI builds as well.

[projectgus]

These commits have been cherry-picked, thanks @paulreimer!