Add options to disable some newlibfunctionalities

[fjtrujy]

Description

The main scope of this PR is to allow the user to disable some concrete newlib/POSIX features to save RAM.
This is just for advanced users that understand what is going under the crt0 and libcglue initialization.

I have added a new example where we see how we can reduce a dummy hello world.

int main(int argc, char** argv) {
    while(1) { printf("Hello World!\n"); }
    return 0;
}

From EBOOT.PBP with 126664 bytes:

-rw-r--r--  1 fjtrujy  staff  126664 Nov 29 17:29 EBOOT.PBP
-rw-r--r--  1 fjtrujy  staff     328 Nov 29 17:27 Makefile.sample
-rw-r--r--  1 fjtrujy  staff     324 Nov 29 17:29 PARAM.SFO
-rwxr-xr-x  1 fjtrujy  staff  126300 Nov 29 17:29 light_size.elf
-rw-r--r--  1 fjtrujy  staff    1167 Nov 29 17:29 main.c
-rw-r--r--  1 fjtrujy  staff    2140 Nov 29 17:29 main.o

To EBOOT.PBP with 50532 bytes:

-rw-r--r--  1 fjtrujy  staff  50532 Nov 29 18:22 EBOOT.PBP
-rw-r--r--  1 fjtrujy  staff    328 Nov 29 18:31 Makefile.sample
-rw-r--r--  1 fjtrujy  staff    324 Nov 29 18:22 PARAM.SFO
-rwxr-xr-x  1 fjtrujy  staff  50168 Nov 29 18:22 light_size.elf
-rw-r--r--  1 fjtrujy  staff   1176 Nov 29 18:31 main.c
-rw-r--r--  1 fjtrujy  staff   5052 Nov 29 18:22 main.o

Just putting in your main.c file:

#include <sys/socket.h>
#include <errno.h>

PSP_DISABLE_NEWLIB_PIPE_SUPPORT()
PSP_DISABLE_NEWLIB_SOCKET_SUPPORT()
PSP_DISABLE_NEWLIB_TIMEZONE_SUPPORT()
PSP_DISABLE_NEWLIB_CWD_SUPPORT()
PSP_DISABLE_AUTOSTART_PTHREAD()

Cheers

[diamant3]

This is a really nice improvement, fjtrujy! approved to me.

Just a side question, Can you do it using a makefile instead of putting it in a code?

[sharkwouter]

Honestly, I'd argue it is nicer to have it in the code. This looks like a fine change to me, but I did not test it yet.