Disable multiple C stub functions

[samhocevar]

One of the root problems is that the PlayStation does not have <signal.h>, so we need to disable this header in gcc_linux_amd64.c. But then it also makes sense to disable it in gcc_linux_arm64.c since it’ll just call stubs anyway.

Other parts of the Go runtime use networking-related headers such as <netdb.h> or <netinet/in.h> to retrieve constants, so these need to be disabled for the PlayStation compiler, too.

We can actually do the same for calls to e.g. setenv, or setgid, etc. In the end, it is possible to get rid of all C stubs in hitsumabushi_syscalls_linux.c.

This was successfully tested with the following setups:

• Nintendo Switch (with native clang.exe from NDK 15.2)
• PS4 (with native clang.exe from SDK 10.000)
• PS5 (with native clang.exe from SDK 5.000)