macOS: disable CONFIDENTIAL='__attribute__((section("confidential")))' on emulator build

[trezor]

macOS: disable CONFIDENTIAL='__attribute__((section("confidential")))' on emulator build

[malinah]

I'm proposing this fix:

#ifdef __MACH__
#define CONFIDENTIAL_SECTION "__DATA,confidential"
#else
#define CONFIDENTIAL_SECTION "confidential"
#endif

#define CONFIDENTIAL __attribute__((section((CONFIDENTIAL_SECTION))))

Unfortunately the fix requires structural changes to the source code since it's not a plain definition that can be passed through gcc -D option as it is now in Makefile.include.

Can't validate on macOS due to build errors:

• Build system is confusing python2 and python3 scripts.
• Directory missing /usr/include.
• Missing objcopy.
  ...

Decide wether legacy should be supported on macOS.